avr-libc - de Smith and Manuals/avr...ii CONTENTS Contents 1 AVR Libc 1 1.1 Introduction. . . . . ....

avr-libc1.8.1

Generated by Doxygen 1.8.7

Tue Aug 12 2014 21:20:45

ii CONTENTS

Contents

1 AVR Libc 1

1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 General information about this library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.3 Supported Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.4 avr-libc License . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2 Toolchain Overview 11

2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.2 FSF and GNU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.3 GCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.4 GNU Binutils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.5 avr-libc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.6 Building Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.7 AVRDUDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.8 GDB / Insight / DDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.9 AVaRICE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.10 SimulAVR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.11 Utilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.12 Toolchain Distributions (Distros) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.13 Open Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3 Memory Areas and Using malloc() 15

3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.2 Internal vs. external RAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.3 Tunables for malloc() . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.4 Implementation details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4 Memory Sections 18

4.1 The .text Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4.2 The .data Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4.3 The .bss Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4.4 The .eeprom Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4.5 The .noinit Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4.6 The .initN Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4.7 The .finiN Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.8 Using Sections in Assembler Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4.9 Using Sections in C Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Generated on Tue Aug 12 2014 21:20:45 for avr-libc by Doxygen

CONTENTS iii

5 Data in Program Space 22

5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

5.2 A Note On const . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

5.3 Storing and Retrieving Data in the Program Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

5.4 Storing and Retrieving Strings in the Program Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

5.5 Caveats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

6 avr-libc and assembler programs 26

6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

6.2 Invoking the compiler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

6.3 Example program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

6.4 Pseudo-ops and operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

7 Inline Assembler Cookbook 30

7.1 GCC asm Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

7.2 Assembler Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

7.3 Input and Output Operands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

7.4 Clobbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

7.5 Assembler Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

7.6 C Stub Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

7.7 C Names Used in Assembler Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

7.8 Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

8 How to Build a Library 39

8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

8.2 How the Linker Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

8.3 How to Design a Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

8.4 Creating a Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

8.5 Using a Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

9 Benchmarks 42

9.1 A few of libc functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

9.2 Math functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

10 Porting From IAR to AVR GCC 44

10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

10.2 Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

10.3 Interrupt Service Routines (ISRs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

10.4 Intrinsic Routines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46


iv CONTENTS

10.5 Flash Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

10.6 Non-Returning main() . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

10.7 Locking Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

11 Frequently Asked Questions 48

11.1 FAQ Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

11.2 My program doesn’t recognize a variable updated within an interrupt routine . . . . . . . . . . . . . . . 49

11.3 I get "undefined reference to..." for functions like "sin()" . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

11.4 How to permanently bind a variable to a register? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

11.5 How to modify MCUCR or WDTCR early? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

11.6 What is all this _BV() stuff about? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

11.7 Can I use C++ on the AVR? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

11.8 Shouldn’t I initialize all my variables? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

11.9 Why do some 16-bit timer registers sometimes get trashed? . . . . . . . . . . . . . . . . . . . . . . . . 52

11.10How do I use a #define’d constant in an asm statement? . . . . . . . . . . . . . . . . . . . . . . . . . . 52

11.11Why does the PC randomly jump around when single-stepping through my program in avr-gdb? . . . . . 53

11.12How do I trace an assembler file in avr-gdb? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

11.13How do I pass an IO port as a parameter to a function? . . . . . . . . . . . . . . . . . . . . . . . . . . 54

11.14What registers are used by the C compiler? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

11.15How do I put an array of strings completely in ROM? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

11.16How to use external RAM? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

11.17Which -O flag to use? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

11.18How do I relocate code to a fixed address? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

11.19My UART is generating nonsense! My ATmega128 keeps crashing! Port F is completely broken! . . . . 60

11.20Why do all my "foo...bar" strings eat up the SRAM? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

11.21Why does the compiler compile an 8-bit operation that uses bitwise operators into a 16-bit operation inassembly? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

11.22How to detect RAM memory and variable overlap problems? . . . . . . . . . . . . . . . . . . . . . . . 61

11.23Is it really impossible to program the ATtinyXX in C? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

11.24What is this "clock skew detected" message? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

11.25Why are (many) interrupt flags cleared by writing a logical 1? . . . . . . . . . . . . . . . . . . . . . . . 62

11.26Why have "programmed" fuses the bit value 0? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

11.27Which AVR-specific assembler operators are available? . . . . . . . . . . . . . . . . . . . . . . . . . . 63

11.28Why are interrupts re-enabled in the middle of writing the stack pointer? . . . . . . . . . . . . . . . . . . 63

11.29Why are there five different linker scripts? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

11.30How to add a raw binary image to linker output? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

11.31How do I perform a software reset of the AVR? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

11.32I am using floating point math. Why is the compiled code so big? Why does my code not work? . . . . . 65


CONTENTS v

11.33What pitfalls exist when writing reentrant code? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

11.34Why are some addresses of the EEPROM corrupted (usually address zero)? . . . . . . . . . . . . . . . 68

11.35Why is my baud rate wrong? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

11.36On a device with more than 128 KiB of flash, how to make function pointers work? . . . . . . . . . . . . 68

11.37Why is assigning ports in a "chain" a bad idea? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

12 Building and Installing the GNU Tool Chain 69

12.1 Building and Installing under Linux, FreeBSD, and Others . . . . . . . . . . . . . . . . . . . . . . . . . 69

12.2 Required Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

12.3 Optional Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

12.4 GNU Binutils for the AVR target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

12.5 GCC for the AVR target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

12.6 AVR LibC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

12.7 AVRDUDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

12.8 GDB for the AVR target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

12.9 SimulAVR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

12.10AVaRICE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

12.11Building and Installing under Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

12.12Tools Required for Building the Toolchain for Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

12.13Building the Toolchain for Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

13 Using the GNU tools 81

13.1 Options for the C compiler avr-gcc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

13.1.1 Machine-specific options for the AVR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

13.1.2 Selected general compiler options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

13.2 Options for the assembler avr-as . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

13.2.1 Machine-specific assembler options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

13.2.2 Examples for assembler options passed through the C compiler . . . . . . . . . . . . . . . . . 96

13.3 Controlling the linker avr-ld . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

13.3.1 Selected linker options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

13.3.2 Passing linker options from the C compiler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

14 Compiler optimization 98

14.1 Problems with reordering code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

15 Using the avrdude program 99

16 Release Numbering and Methodology 101

16.1 Release Version Numbering Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101


vi CONTENTS

16.2 Releasing AVR Libc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

16.2.1 Creating an SVN branch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

16.2.2 Making a release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

17 Acknowledgments 103

18 Todo List 104

19 Deprecated List 104

20 Module Index 105

20.1 Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

21 Data Structure Index 106

21.1 Data Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

22 File Index 107

22.1 File List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

23 Module Documentation 111

23.1 <alloca.h>: Allocate space in the stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

23.1.1 Detailed Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

23.1.2 Function Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

23.2 <assert.h>: Diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112


23.2.2 Macro Definition Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

23.3 <ctype.h>: Character Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113



23.4 <errno.h>: System Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115



23.5 <inttypes.h>: Integer Type conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116



23.5.3 Typedef Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

23.6 <math.h>: Mathematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127





CONTENTS vii

23.7 <setjmp.h>: Non-local goto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137



23.8 <stdint.h>: Standard Integer Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139




23.9 <stdio.h>: Standard IO facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149





23.10<stdlib.h>: General utilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163





23.10.5 Variable Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

23.11<string.h>: Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172




23.12<time.h>: Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182




23.12.4 Enumeration Type Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185


23.13<avr/boot.h>: Bootloader Support Utilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190



23.14<avr/cpufunc.h>: Special AVR CPU functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196



23.15<avr/eeprom.h>: EEPROM handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197




viii CONTENTS


23.16<avr/fuse.h>: Fuse Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201

23.17<avr/interrupt.h>: Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204



23.18<avr/io.h>: AVR device-specific IO definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222



23.19<avr/lock.h>: Lockbit Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224

23.20<avr/pgmspace.h>: Program Space Utilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226





23.21<avr/power.h>: Power Reduction Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239

23.22Additional notes from <avr/sfr_defs.h> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252

23.23<avr/sfr_defs.h>: Special function registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253



23.24<avr/signature.h>: Signature Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255

23.25<avr/sleep.h>: Power Management and Sleep Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . 256



23.26<avr/version.h>: avr-libc version macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258



23.27<avr/wdt.h>: Watchdog timer handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260



23.28<util/atomic.h> Atomically and Non-Atomically Executed Code Blocks . . . . . . . . . . . . . . . . . . 263



23.29<util/crc16.h>: CRC Computations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266



23.30<util/delay.h>: Convenience functions for busy-wait delay loops . . . . . . . . . . . . . . . . . . . . . . 270



CONTENTS ix


23.31<util/delay_basic.h>: Basic busy-wait delay loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272



23.32<util/parity.h>: Parity bit generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273



23.33<util/setbaud.h>: Helper macros for baud rate calculations . . . . . . . . . . . . . . . . . . . . . . . . 274



23.34<util/twi.h>: TWI bit mask definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276



23.35<compat/deprecated.h>: Deprecated items . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280




23.36<compat/ina90.h>: Compatibility with IAR EWB 3.x . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283

23.37Demo projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284


23.38Combining C and assembly source files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285

23.38.1 Hardware setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285

23.38.2 A code walkthrough . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285

23.38.3 The source code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287

23.39A simple project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288

23.39.1 The Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288

23.39.2 The Source Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289

23.39.3 Compiling and Linking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291

23.39.4 Examining the Object File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291

23.39.5 Linker Map Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295

23.39.6 Generating Intel Hex Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297

23.39.7 Letting Make Build the Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297

23.39.8 Reference to the source code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299

23.40A more sophisticated project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300

23.40.1 Hardware setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300

23.40.2 Functional overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302



x CONTENTS

23.40.4 The source code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305

23.41Using the standard IO facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306

23.41.1 Hardware setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306

23.41.2 Functional overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307


23.41.4 The source code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311

23.42Example using the two-wire interface (TWI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312

23.42.1 Introduction into TWI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312

23.42.2 The TWI example project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312

23.42.3 The Source Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312

24 Data Structure Documentation 316

24.1 atexit_s Struct Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316

24.2 div_t Struct Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316


24.2.2 Field Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316

24.3 ldiv_t Struct Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316


24.3.2 Field Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317

24.4 tm Struct Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317


24.5 week_date Struct Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318


25 File Documentation 318

25.1 assert.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318

25.2 atoi.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318

25.3 atol.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318

25.4 atomic.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318

25.5 boot.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318


25.6 cpufunc.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323

25.7 crc16.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323

25.8 ctype.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324

25.9 delay.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324

25.10delay_basic.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324

25.11errno.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325

25.12fdevopen.c File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326


CONTENTS xi

25.13ffs.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326

25.14ffsl.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326

25.15ffsll.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326

25.16fuse.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326

25.17interrupt.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326


25.18inttypes.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327

25.19io.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329

25.20lock.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329

25.21math.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329

25.22memccpy.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

25.23memchr.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

25.24memchr_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

25.25memcmp.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

25.26memcmp_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

25.27memcmp_PF.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

25.28memcpy.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

25.29memcpy_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

25.30memmem.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

25.31memmove.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

25.32memrchr.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

25.33memrchr_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

25.34memset.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

25.35parity.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

25.36pgmspace.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332


25.37power.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340

25.38setbaud.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341

25.39setjmp.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341

25.40signature.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341

25.41sleep.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341

25.42stdint.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342

25.43stdio.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344

25.44stdlib.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346

25.45strcasecmp.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348

25.46strcasecmp_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348

25.47strcasestr.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348


xii CONTENTS

25.48strcat.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348

25.49strcat_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348

25.50strchr.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348

25.51strchr_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348

25.52strchrnul.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348

25.53strchrnul_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348

25.54strcmp.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348

25.55strcmp_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348

25.56strcpy.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348

25.57strcpy_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348

25.58strcspn.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348

25.59strcspn_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348

25.60strdup.c File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348

25.61string.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349

25.62strlcat.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.63strlcat_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.64strlcpy.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.65strlcpy_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.66strlen.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.67strlen_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.68strlwr.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.69strncasecmp.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.70strncasecmp_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.71strncat.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.72strncat_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.73strncmp.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.74strncmp_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.75strncpy.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.76strncpy_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.77strnlen.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.78strnlen_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.79strpbrk.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.80strpbrk_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.81strrchr.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.82strrchr_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.83strrev.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.84strsep.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350


1 AVR Libc 1

25.85strsep_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

25.86strspn.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351

25.87strspn_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351

25.88strstr.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351

25.89strstr_P.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351

25.90strtok.c File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351

25.91strtok_P.c File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351

25.92strtok_r.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351

25.93strtok_rP.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351

25.94strupr.S File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351

25.95time.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351

25.96twi.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353

25.97wdt.h File Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354

Index 355

1 AVR Libc

1.1 Introduction

The latest version of this document is always available from http://savannah.nongnu.org/projects/avr-libc/

The AVR Libc package provides a subset of the standard C library for Atmel AVR 8-bit RISC microcontrollers.In addition, the library provides the basic startup code needed by most applications.

There is a wealth of information in this document which goes beyond simply describing the interfaces and routinesprovided by the library. We hope that this document provides enough information to get a new AVR developer up tospeed quickly using the freely available development tools: binutils, gcc avr-libc and many others.

If you find yourself stuck on a problem which this document doesn’t quite address, you may wish to post a messageto the avr-gcc mailing list. Most of the developers of the AVR binutils and gcc ports in addition to the devleopers ofavr-libc subscribe to the list, so you will usually be able to get your problem resolved. You can subscribe to the list athttp://lists.nongnu.org/mailman/listinfo/avr-gcc-list . Before posting to the list, you mightwant to try reading the Frequently Asked Questions chapter of this document.

Note

If you think you’ve found a bug, or have a suggestion for an improvement, either in this documentation or in the li-brary itself, please use the bug tracker at https://savannah.nongnu.org/bugs/?group=avr-libcto ensure the issue won’t be forgotten.

1.2 General information about this library

In general, it has been the goal to stick as best as possible to established standards while implementing this library.Commonly, this refers to the C library as described by the ANSI X3.159-1989 and ISO/IEC 9899:1990 ("ANSI-C")standard, as well as parts of their successor ISO/IEC 9899:1999 ("C99"). Some additions have been inspired byother standards like IEEE Std 1003.1-1988 ("POSIX.1"), while other extensions are purely AVR-specific (like the entireprogram-space string interface).


http://savannah.nongnu.org/projects/avr-libc/

http://www.atmel.com/products/AVR/

http://lists.nongnu.org/mailman/listinfo/avr-gcc-list

https://savannah.nongnu.org/bugs/?group=avr-libc

2 CONTENTS

Unless otherwise noted, functions of this library are not guaranteed to be reentrant. In particular, any functions that storelocal state are known to be non-reentrant, as well as functions that manipulate IO registers like the EEPROM accessroutines. If these functions are used within both standard and interrupt contexts undefined behaviour will result. See theFAQ for a more detailed discussion.

1.3 Supported Devices

The following is a list of AVR devices currently supported by the library. Note that actual support for some newer devicesdepends on the ability of the compiler/assembler to support these devices at library compile-time.

megaAVR Devices:

• atmega103

• atmega128

• atmega128a

• atmega1280

• atmega1281

• atmega1284

• atmega1284p

• atmega16

• atmega161

• atmega162

• atmega163

• atmega164a

• atmega164p

• atmega164pa

• atmega165

• atmega165a

• atmega165p

• atmega165pa

• atmega168

• atmega168a

• atmega168p

• atmega168pa

• atmega16a

• atmega2560


1.3 Supported Devices 3

• atmega2561

• atmega32

• atmega32a

• atmega323

• atmega324a

• atmega324p

• atmega324pa

• atmega325

• atmega325a

• atmega325p

• atmega325pa

• atmega3250

• atmega3250a

• atmega3250p

• atmega3250pa

• atmega328

• atmega328p

• atmega48

• atmega48a

• atmega48pa

• atmega48p

• atmega64

• atmega64a

• atmega640

• atmega644

• atmega644a

• atmega644p

• atmega644pa

• atmega645

• atmega645a

• atmega645p

• atmega6450

• atmega6450a


4 CONTENTS

• atmega6450p

• atmega8

• atmega8a

• atmega88

• atmega88a

• atmega88p

• atmega88pa

• atmega8515

• atmega8535

tinyAVR Devices:

• attiny4

• attiny5

• attiny10

• attiny11 [1]

• attiny12 [1]

• attiny13

• attiny13a

• attiny15 [1]

• attiny20

• attiny22

• attiny24

• attiny24a

• attiny25

• attiny26

• attiny261

• attiny261a

• attiny28 [1]

• attiny2313

• attiny2313a

• attiny40

• attiny4313

• attiny43u



• attiny44

• attiny44a

• attiny45

• attiny461

• attiny461a

• attiny48

• attiny828

• attiny84

• attiny84a

• attiny85

• attiny861

• attiny861a

• attiny87

• attiny88

• attiny1634

Automotive AVR Devices:

• atmega16m1

• atmega32c1

• atmega32m1

• atmega64c1

• atmega64m1

• attiny167

• ata5505

• ata5272

• ata5790

• ata5795

CAN AVR Devices:

• at90can32

• at90can64

• at90can128


6 CONTENTS

LCD AVR Devices:

• atmega169

• atmega169a

• atmega169p

• atmega169pa

• atmega329

• atmega329a

• atmega329p

• atmega329pa

• atmega3290

• atmega3290a

• atmega3290p

• atmega3290pa

• atmega649

• atmega649a

• atmega6490

• atmega6490a

• atmega6490p

• atmega649p

Lighting AVR Devices:

• at90pwm1

• at90pwm2

• at90pwm2b

• at90pwm216

• at90pwm3

• at90pwm3b

• at90pwm316

• at90pwm161

• at90pwm81

Smart Battery AVR Devices:



• atmega8hva

• atmega16hva

• atmega16hva2

• atmega16hvb

• atmega16hvbrevb

• atmega32hvb

• atmega32hvbrevb

• atmega64hve

• atmega406

USB AVR Devices:

• at90usb82

• at90usb162

• at90usb646

• at90usb647

• at90usb1286

• at90usb1287

• atmega8u2

• atmega16u2

• atmega16u4

• atmega32u2

• atmega32u4

• atmega32u6

XMEGA Devices:

• atxmega16a4

• atxmega16a4u

• atxmega16c4

• atxmega16d4

• atxmega32a4

• atxmega32a4u

• atxmega32c4


8 CONTENTS

• atxmega32d4

• atxmega64a1

• atxmega64a1u

• atxmega64a3

• atxmega64a3u

• atxmega64a4u

• atxmega64b1

• atxmega64b3

• atxmega64c3

• atxmega64d3

• atxmega64d4

• atxmega128a1

• atxmega128a1u

• atxmega128a3

• atxmega128a3u

• atxmega128a4u

• atxmega128b1

• atxmega128b3

• atxmega128c3

• atxmega128d3

• atxmega128d4

• atxmega192a3

• atxmega192a3u

• atxmega192c3

• atxmega192d3

• atxmega256a3

• atxmega256a3u

• atxmega256a3b

• atxmega256a3bu

• atxmega256c3

• atxmega256d3

• atxmega384c3

• atxmega384d3



Wireless AVR devices:

-atmega644rfr2 -atmega64rfr2 -atmega128rfa1 -atmega1284rfr2 -atmega128rfr2 -atmega2564rfr2 -atmega256rfr2

Miscellaneous Devices:

• at94K [2]

• at76c711 [3]

• at43usb320

• at43usb355

• at86rf401

• at90scr100

• ata6285

• ata6286

• ata6289

• m3000 [4]

Classic AVR Devices:

• at90s1200 [1]

• at90s2313

• at90s2323

• at90s2333

• at90s2343

• at90s4414

• at90s4433

• at90s4434

• at90s8515

• at90c8534

• at90s8535

Note

[1] Assembly only. There is no direct support for these devices to be programmed in C since they do not have aRAM based stack. Still, it could be possible to program them in C, see the FAQ for an option.


10 CONTENTS

Note

[2] The at94K devices are a combination of FPGA and AVR microcontroller. [TRoth-2002/11/12: Not sure of thelevel of support for these. More information would be welcomed.]

Note

[3] The at76c711 is a USB to fast serial interface bridge chip using an AVR core.

Note

[4] The m3000 is a motor controller AVR ASIC from Intelligent Motion Systems (IMS) / Schneider Electric.

1.4 avr-libc License

avr-libc can be freely used and redistributed, provided the following license conditions are met.

Portions of avr-libc are Copyright (c) 1999-2010Werner Boellmann,Dean Camera,Pieter Conradie,Brian Dean,Keith Gudger,Wouter van Gulik,Bjoern Haase,Steinar Haugen,Peter Jansen,Reinhard Jessich,Magnus Johansson,Harald Kipp,Carlos Lamas,Cliff Lawson,Artur Lipowski,Marek Michalkiewicz,Todd C. Miller,Rich Neswold,Colin O’Flynn,Bob Paddock,Andrey Pashchenko,Reiner Patommel,Florin-Viorel Petrov,Alexander Popov,Michael Rickman,Theodore A. Roth,Juergen Schilling,Philip Soeberg,Anatoly Sokolov,Nils Kristian Strom,Michael Stumpf,Stefan Swanepoel,Helmut Wallner,Eric B. Weddington,Joerg Wunsch,Dmitry Xmelkov,Atmel Corporation,egnite Software GmbH,The Regents of the University of California.All rights reserved.

Redistribution and use in source and binary forms, with or withoutmodification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright


2 Toolchain Overview 11

notice, this list of conditions and the following disclaimer.

* Redistributions in binary form must reproduce the above copyrightnotice, this list of conditions and the following disclaimer inthe documentation and/or other materials provided with thedistribution.

* Neither the name of the copyright holders nor the names ofcontributors may be used to endorse or promote products derivedfrom this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THEIMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSEARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BELIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, ORCONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OFSUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESSINTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER INCONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THEPOSSIBILITY OF SUCH DAMAGE.

2 Toolchain Overview

2.1 Introduction

Welcome to the open source software development toolset for the Atmel AVR!

There is not a single tool that provides everything needed to develop software for the AVR. It takes many tools workingtogether. Collectively, the group of tools are called a toolset, or commonly a toolchain, as the tools are chained togetherto produce the final executable application for the AVR microcontroller.

The following sections provide an overview of all of these tools. You may be used to cross-compilers that provideeverything with a GUI front-end, and not know what goes on "underneath the hood". You may be coming from a desktopor server computer background and not used to embedded systems. Or you may be just learning about the mostcommon software development toolchain available on Unix and Linux systems. Hopefully the following overview will behelpful in putting everything in perspective.

2.2 FSF and GNU

According to its website, "the Free Software Foundation (FSF), established in 1985, is dedicated to promoting computerusers’ rights to use, study, copy, modify, and redistribute computer programs. The FSF promotes the development anduse of free software, particularly the GNU operating system, used widely in its GNU/Linux variant." The FSF remainsthe primary sponsor of the GNU project.

The GNU Project was launched in 1984 to develop a complete Unix-like operating system which is free software: theGNU system. GNU is a recursive acronym for »GNU’s Not Unix«; it is pronounced guh-noo, approximately like canoe.

One of the main projects of the GNU system is the GNU Compiler Collection, or GCC, and its sister project, GNUBinutils. These two open source projects provide a foundation for a software development toolchain. Note that theseprojects were designed to originally run on Unix-like systems.

2.3 GCC

GCC stands for GNU Compiler Collection. GCC is highly flexible compiler system. It has different compiler front-endsfor different languages. It has many back-ends that generate assembly code for many different processors and host


12 CONTENTS

operating systems. All share a common "middle-end", containing the generic parts of the compiler, including a lot ofoptimizations.

In GCC, a host system is the system (processor/OS) that the compiler runs on. A target system is the system thatthe compiler compiles code for. And, a build system is the system that the compiler is built (from source code) on. If acompiler has the same system for host and for target, it is known as a native compiler. If a compiler has different systemsfor host and target, it is known as a cross-compiler. (And if all three, build, host, and target systems are different, it isknown as a Canadian cross compiler, but we won’t discuss that here.) When GCC is built to execute on a host systemsuch as FreeBSD, Linux, or Windows, and it is built to generate code for the AVR microcontroller target, then it is a crosscompiler, and this version of GCC is commonly known as "AVR GCC". In documentation, or discussion, AVR GCC isused when referring to GCC targeting specifically the AVR, or something that is AVR specific about GCC. The term"GCC" is usually used to refer to something generic about GCC, or about GCC as a whole.

GCC is different from most other compilers. GCC focuses on translating a high-level language to the target assemblyonly. AVR GCC has three available compilers for the AVR: C language, C++, and Ada. The compiler itself does notassemble or link the final code.

GCC is also known as a "driver" program, in that it knows about, and drives other programs seamlessly to create thefinal output. The assembler, and the linker are part of another open source project called GNU Binutils. GCC knowshow to drive the GNU assembler (gas) to assemble the output of the compiler. GCC knows how to drive the GNU linker(ld) to link all of the object modules into a final executable.

The two projects, GCC and Binutils, are very much interrelated and many of the same volunteers work on both opensource projects.

When GCC is built for the AVR target, the actual program names are prefixed with "avr-". So the actual executable namefor AVR GCC is: avr-gcc. The name "avr-gcc" is used in documentation and discussion when referring to the programitself and not just the whole AVR GCC system.

See the GCC Web Site and GCC User Manual for more information about GCC.

2.4 GNU Binutils

The name GNU Binutils stands for "Binary Utilities". It contains the GNU assembler (gas), and the GNU linker (ld),but also contains many other utilities that work with binary files that are created as part of the software developmenttoolchain.

Again, when these tools are built for the AVR target, the actual program names are prefixed with "avr-". For example,the assembler program name, for a native assembler is "as" (even though in documentation the GNU assembler iscommonly referred to as "gas"). But when built for an AVR target, it becomes "avr-as". Below is a list of the programsthat are included in Binutils:

avr-as

The Assembler.

avr-ld

The Linker.

avr-ar

Create, modify, and extract from libraries (archives).

avr-ranlib

Generate index to library (archive) contents.

avr-objcopy

Copy and translate object files to different formats.


2.5 avr-libc 13

avr-objdump

Display information from object files including disassembly.

avr-size

List section sizes and total size.

avr-nm

List symbols from object files.

avr-strings

List printable strings from files.

avr-strip

Discard symbols from files.

avr-readelf

Display the contents of ELF format files.

avr-addr2line

Convert addresses to file and line.

avr-c++filt

Filter to demangle encoded C++ symbols.

2.5 avr-libc

GCC and Binutils provides a lot of the tools to develop software, but there is one critical component that they do notprovide: a Standard C Library.

There are different open source projects that provide a Standard C Library depending upon your system time, whetherfor a native compiler (GNU Libc), for some other embedded system (newlib), or for some versions of Linux (uCLibc).The open source AVR toolchain has its own Standard C Library project: avr-libc.

AVR-Libc provides many of the same functions found in a regular Standard C Library and many additional libraryfunctions that is specific to an AVR. Some of the Standard C Library functions that are commonly used on a PCenvironment have limitations or additional issues that a user needs to be aware of when used on an embedded system.

AVR-Libc also contains the most documentation about the whole AVR toolchain.

2.6 Building Software

Even though GCC, Binutils, and avr-libc are the core projects that are used to build software for the AVR, there is anotherpiece of software that ties it all together: Make. GNU Make is a program that makes things, and mainly software. Makeinterprets and executes a Makefile that is written for a project. A Makefile contains dependency rules, showing whichoutput files are dependent upon which input files, and instructions on how to build output files from input files.

Some distributions of the toolchains, and other AVR tools such as MFile, contain a Makefile template written for the AVRtoolchain and AVR applications that you can copy and modify for your application.

See the GNU Make User Manual for more information.


14 CONTENTS

2.7 AVRDUDE

After creating your software, you’ll want to program your device. You can do this by using the program AVRDUDE whichcan interface with various hardware devices to program your processor.

AVRDUDE is a very flexible package. All the information about AVR processors and various hardware programmers isstored in a text database. This database can be modified by any user to add new hardware or to add an AVR processorif it is not already listed.

2.8 GDB / Insight / DDD

The GNU Debugger (GDB) is a command-line debugger that can be used with the rest of the AVR toolchain. Insightis GDB plus a GUI written in Tcl/Tk. Both GDB and Insight are configured for the AVR and the main executables areprefixed with the target name: avr-gdb, and avr-insight. There is also a "text mode" GUI for GDB: avr-gdbtui. DDD (DataDisplay Debugger) is another popular GUI front end to GDB, available on Unix and Linux systems.

2.9 AVaRICE

AVaRICE is a back-end program to AVR GDB and interfaces to the Atmel JTAG In-Circuit Emulator (ICE), to provideemulation capabilities.

2.10 SimulAVR

SimulAVR is an AVR simulator used as a back-end with AVR GDB. Unfortunately, this project is currently unmaintainedand could use some help.

2.11 Utilities

There are also other optional utilities available that may be useful to add to your toolset.

SRecord is a collection of powerful tools for manipulating EPROM load files. It reads and writes numerous EPROMfile formats, and can perform many different manipulations.

MFile is a simple Makefile generator is meant as an aid to quickly customize a Makefile to use for your AVR application.

2.12 Toolchain Distributions (Distros)

All of the various open source projects that comprise the entire toolchain are normally distributed as source code. It isleft up to the user to build the tool application from its source code. This can be a very daunting task to any potentialuser of these tools.

Luckily there are people who help out in this area. Volunteers take the time to build the application from source code onparticular host platforms and sometimes packaging the tools for convenient installation by the end user. These packagescontain the binary executables of the tools, pre-made and ready to use. These packages are known as "distributions" ofthe AVR toolchain, or by a more shortened name, "distros".

AVR toolchain distros are available on FreeBSD, Windows, Mac OS X, and certain flavors of Linux.


2.13 Open Source 15

2.13 Open Source

All of these tools, from the original source code in the multitude of projects, to the various distros, are put together bymany, many volunteers. All of these projects could always use more help from other people who are willing to volunteersome of their time. There are many different ways to help, for people with varying skill levels, abilities, and availabletime.

You can help to answer questions in mailing lists such as the avr-gcc-list, or on forums at the AVR Freaks website. Thishelps many people new to the open source AVR tools.

If you think you found a bug in any of the tools, it is always a big help to submit a good bug report to the proper project.A good bug report always helps other volunteers to analyze the problem and to get it fixed for future versions of thesoftware.

You can also help to fix bugs in various software projects, or to add desirable new features.

Volunteers are always welcome! :-)

3 Memory Areas and Using malloc()

3.1 Introduction

Many of the devices that are possible targets of avr-libc have a minimal amount of RAM. The smallest parts supported bythe C environment come with 128 bytes of RAM. This needs to be shared between initialized and uninitialized variables(sections .data and .bss), the dynamic memory allocator, and the stack that is used for calling subroutines and storinglocal (automatic) variables.

Also, unlike larger architectures, there is no hardware-supported memory management which could help in separatingthe mentioned RAM regions from being overwritten by each other.

The standard RAM layout is to place .data variables first, from the beginning of the internal RAM, followed by .bss.The stack is started from the top of internal RAM, growing downwards. The so-called "heap" available for the dynamicmemory allocator will be placed beyond the end of .bss. Thus, there’s no risk that dynamic memory will ever collide withthe RAM variables (unless there were bugs in the implementation of the allocator). There is still a risk that the heapand stack could collide if there are large requirements for either dynamic memory or stack space. The former can evenhappen if the allocations aren’t all that large but dynamic memory allocations get fragmented over time such that newrequests don’t quite fit into the "holes" of previously freed regions. Large stack space requirements can arise in a Cfunction containing large and/or numerous local variables or when recursively calling function.


16 CONTENTS

Note

The pictures shown in this document represent typical situations where the RAM locations refer to an ATmega128.The memory addresses used are not displayed in a linear scale.

!

__bss_end

__data_end == __bss_start

__data_start

RAMENDSP

*(__malloc_heap_start) == __heap_start

*(__brkval) (<= *SP − *(__malloc_margin))

variablesvariables

.data .bss

0x10F

F

0x0100

heap stack

on−board RAM external RAM

0x1100

0xF

FF

F

Figure 1: RAM map of a device with internal RAM

On a simple device like a microcontroller it is a challenge to implement a dynamic memory allocator that is simple enoughso the code size requirements will remain low, yet powerful enough to avoid unnecessary memory fragmentation andto get it all done with reasonably few CPU cycles. Microcontrollers are often low on space and also run at much lowerspeeds than the typical PC these days.

The memory allocator implemented in avr-libc tries to cope with all of these constraints, and offers some tuning optionsthat can be used if there are more resources available than in the default configuration.

3.2 Internal vs. external RAM

Obviously, the constraints are much harder to satisfy in the default configuration where only internal RAM is available.Extreme care must be taken to avoid a stack-heap collision, both by making sure functions aren’t nesting too deeply, anddon’t require too much stack space for local variables, as well as by being cautious with allocating too much dynamicmemory.

If external RAM is available, it is strongly recommended to move the heap into the external RAM, regardless of whetheror not the variables from the .data and .bss sections are also going to be located there. The stack should always be keptin internal RAM. Some devices even require this, and in general, internal RAM can be accessed faster since no extrawait states are required. When using dynamic memory allocation and stack and heap are separated in distinct memoryareas, this is the safest way to avoid a stack-heap collision.

3.3 Tunables for malloc()

There are a number of variables that can be tuned to adapt the behavior of malloc() to the expected requirements andconstraints of the application. Any changes to these tunables should be made before the very first call to malloc(). Notethat some library functions might also use dynamic memory (notably those from the <stdio.h>: Standard IO facilities),so make sure the changes will be done early enough in the startup sequence.

The variables __malloc_heap_start and __malloc_heap_end can be used to restrict the malloc() functionto a certain memory region. These variables are statically initialized to point to __heap_start and __heap_end,respectively, where __heap_start is filled in by the linker to point just beyond .bss, and __heap_end is set to 0which makes malloc() assume the heap is below the stack.

If the heap is going to be moved to external RAM, __malloc_heap_end must be adjusted accordingly. This can


3.3 Tunables for malloc() 17

either be done at run-time, by writing directly to this variable, or it can be done automatically at link-time, by adjustingthe value of the symbol __heap_end.

The following example shows a linker command to relocate the entire .data and .bss segments, and the heap to location0x1100 in external RAM. The heap will extend up to address 0xffff.

avr-gcc ... -Wl,--section-start,.data=0x801100,--defsym=__heap_end=0x80ffff ...

Note

See explanation for offset 0x800000. See the chapter about using gcc for the -Wl options.The ld (linker) user manual states that using -Tdata=<x> is equivalent to using –section-start,.data=<x>. How-ever, you have to use –section-start as above because the GCC frontend also sets the -Tdata option for all MCUtypes where the SRAM doesn’t start at 0x800060. Thus, the linker is being faced with two -Tdata options. Sartingwith binutils 2.16, the linker changed the preference, and picks the "wrong" option in this situation.

*(__brkval)

SP

RAMEND

__bss_end


__data_start

*(__malloc_heap_end) == __heap_end


0x1

100

.data

variables

.bss

heap

0xF

FF

F

external RAM

0x1

0F

F

0x0100

stack

on−board RAM

variables

Figure 2: Internal RAM: stack only, external RAM: variables and heap

If dynamic memory should be placed in external RAM, while keeping the variables in internal RAM, something like thefollowing could be used. Note that for demonstration purposes, the assignment of the various regions has not beenmade adjacent in this example, so there are "holes" below and above the heap in external RAM that remain completelyunaccessible by regular variables or dynamic memory allocations (shown in light bisque color in the picture below).

avr-gcc ... -Wl,--defsym=__heap_start=0x802000,--defsym=__heap_end=0x803fff ...

SP

RAMEND

__bss_end


__data_start

*(__malloc_heap_end) == __heap_end

*(__brkval)


0x1

0F

F

0x0

10

0

stack

on−board RAM

0x1

10

0

0xF

FF

F

.data

variablesvariables

.bss

0x3

FF

F

heap

0x2

00

0

external RAM

Figure 3: Internal RAM: variables and stack, external RAM: heap


18 CONTENTS

If __malloc_heap_end is 0, the allocator attempts to detect the bottom of stack in order to prevent a stack-heapcollision when extending the actual size of the heap to gain more space for dynamic memory. It will not try to go beyondthe current stack limit, decreased by __malloc_margin bytes. Thus, all possible stack frames of interrupt routinesthat could interrupt the current function, plus all further nested function calls must not require more stack space, or theywill risk colliding with the data segment.

The default value of __malloc_margin is set to 32.

3.4 Implementation details

Dynamic memory allocation requests will be returned with a two-byte header prepended that records the size of theallocation. This is later used by free(). The returned address points just beyond that header. Thus, if the applicationaccidentally writes before the returned memory region, the internal consistency of the memory allocator is compromised.

The implementation maintains a simple freelist that accounts for memory blocks that have been returned in previouscalls to free(). Note that all of this memory is considered to be successfully added to the heap already, so no furtherchecks against stack-heap collisions are done when recycling memory from the freelist.

The freelist itself is not maintained as a separate data structure, but rather by modifying the contents of the freed memoryto contain pointers chaining the pieces together. That way, no additional memory is reqired to maintain this list exceptfor a variable that keeps track of the lowest memory segment available for reallocation. Since both, a chain pointer andthe size of the chunk need to be recorded in each chunk, the minimum chunk size on the freelist is four bytes.

When allocating memory, first the freelist is walked to see if it could satisfy the request. If there’s a chunk available onthe freelist that will fit the request exactly, it will be taken, disconnected from the freelist, and returned to the caller. If noexact match could be found, the closest match that would just satisfy the request will be used. The chunk will normallybe split up into one to be returned to the caller, and another (smaller) one that will remain on the freelist. In case thischunk was only up to two bytes larger than the request, the request will simply be altered internally to also account forthese additional bytes since no separate freelist entry could be split off in that case.

If nothing could be found on the freelist, heap extension is attempted. This is where __malloc_margin will beconsidered if the heap is operating below the stack, or where __malloc_heap_end will be verified otherwise.

If the remaining memory is insufficient to satisfy the request, NULL will eventually be returned to the caller.

When calling free(), a new freelist entry will be prepared. An attempt is then made to aggregate the new entry withpossible adjacent entries, yielding a single larger entry available for further allocations. That way, the potential for heapfragmentation is hopefully reduced. When deallocating the topmost chunk of memory, the size of the heap is reduced.

A call to realloc() first determines whether the operation is about to grow or shrink the current allocation. When shrinking,the case is easy: the existing chunk is split, and the tail of the region that is no longer to be used is passed to the standardfree() function for insertion into the freelist. Checks are first made whether the tail chunk is large enough to hold a chunkof its own at all, otherwise realloc() will simply do nothing, and return the original region.

When growing the region, it is first checked whether the existing allocation can be extended in-place. If so, this is done,and the original pointer is returned without copying any data contents. As a side-effect, this check will also record thesize of the largest chunk on the freelist.

If the region cannot be extended in-place, but the old chunk is at the top of heap, and the above freelist walk did notreveal a large enough chunk on the freelist to satisfy the new request, an attempt is made to quickly extend this topmostchunk (and thus the heap), so no need arises to copy over the existing data. If there’s no more space available in theheap (same check is done as in malloc()), the entire request will fail.

Otherwise, malloc() will be called with the new request size, the existing data will be copied over, and free() will be calledon the old region.

4 Memory Sections


4.1 The .text Section 19

Remarks

Need to list all the sections which are available to the avr.

Weak Bindings

FIXME: need to discuss the .weak directive.

The following describes the various sections available.

4.1 The .text Section

The .text section contains the actual machine instructions which make up your program. This section is further subdi-vided by the .initN and .finiN sections dicussed below.

Note

The avr-size program (part of binutils), coming from a Unix background, doesn’t account for the .data initial-ization space added to the .text section, so in order to know how much flash the final program will consume, oneneeds to add the values for both, .text and .data (but not .bss), while the amount of pre-allocated SRAM is the sumof .data and .bss.

4.2 The .data Section

This section contains static data which was defined in your code. Things like the following would end up in .data:

char err_str[] = "Your program has died a horrible death!";

struct point pt = { 1, 1 };

It is possible to tell the linker the SRAM address of the beginning of the .data section. This is accomplished by adding-Wl,-Tdata,addr to the avr-gcc command used to the link your program. Not that addr must be offset byadding 0x800000 the to real SRAM address so that the linker knows that the address is in the SRAM memory space.Thus, if you want the .data section to start at 0x1100, pass 0x801100 at the address to the linker. [offset explained]

Note

When using malloc() in the application (which could even happen inside library calls), additional adjustmentsare required.

4.3 The .bss Section

Uninitialized global or static variables end up in the .bss section.

4.4 The .eeprom Section

This is where eeprom variables are stored.

4.5 The .noinit Section

This sections is a part of the .bss section. What makes the .noinit section special is that variables which are defined assuch:


20 CONTENTS

int foo __attribute__ ((section (".noinit")));

will not be initialized to zero during startup as would normal .bss data.

Only uninitialized variables can be placed in the .noinit section. Thus, the following code will cause avr-gcc to issuean error:

int bar __attribute__ ((section (".noinit"))) = 0xaa;

It is possible to tell the linker explicitly where to place the .noinit section by adding -Wl,-section-start=.noinit=0x802000to the avr-gcc command line at the linking stage. For example, suppose you wish to place the .noinit section atSRAM address 0x2000:

$ avr-gcc ... -Wl,--section-start=.noinit=0x802000 ...

Note

Because of the Harvard architecture of the AVR devices, you must manually add 0x800000 to the address youpass to the linker as the start of the section. Otherwise, the linker thinks you want to put the .noinit section into the.text section instead of .data/.bss and will complain.

Alternatively, you can write your own linker script to automate this. [FIXME: need an example or ref to dox for writinglinker scripts.]

4.6 The .initN Sections

These sections are used to define the startup code from reset up through the start of main(). These all are subparts ofthe .text section.

The purpose of these sections is to allow for more specific placement of code within your program.

Note

Sometimes, it is convenient to think of the .initN and .finiN sections as functions, but in reality they are just symbolicnames which tell the linker where to stick a chunk of code which is not a function. Notice that the examples forasm and C can not be called as functions and should not be jumped into.

The .initN sections are executed in order from 0 to 9.

.init0:

Weakly bound to __init(). If user defines __init(), it will be jumped into immediately after a reset.

.init1:

Unused. User definable.

.init2:

In C programs, weakly bound to initialize the stack, and to clear zero_reg (r1).

.init3:



4.7 The .finiN Sections 21

.init4:

For devices with > 64 KB of ROM, .init4 defines the code which takes care of copying the contents of .data from theflash to SRAM. For all other devices, this code as well as the code to zero out the .bss section is loaded from libgcc.a.

.init5:


.init6:

Unused for C programs, but used for constructors in C++ programs.

.init7:


.init8:


.init9:

Jumps into main().

4.7 The .finiN Sections

These sections are used to define the exit code executed after return from main() or a call to exit(). These all aresubparts of the .text section.

The .finiN sections are executed in descending order from 9 to 0.

.finit9:

Unused. User definable. This is effectively where _exit() starts.

.fini8:


.fini7:


.fini6:

Unused for C programs, but used for destructors in C++ programs.

.fini5:


.fini4:


.fini3:



22 CONTENTS

.fini2:


.fini1:


.fini0:

Goes into an infinite loop after program termination and completion of any _exit() code (execution of code in the.fini9 -> .fini1 sections).

4.8 Using Sections in Assembler Code

Example:

#include <avr/io.h>

.section .init1,"ax",@progbitsldi r0, 0xffout _SFR_IO_ADDR(PORTB), r0out _SFR_IO_ADDR(DDRB), r0

Note

The ,"ax",@progbits tells the assembler that the section is allocatable ("a"), executable ("x") and containsdata ("@progbits"). For more detailed information on the .section directive, see the gas user manual.

4.9 Using Sections in C Code

Example:

#include <avr/io.h>

void my_init_portb (void) __attribute__ ((naked)) \__attribute__ ((section (".init3")));

voidmy_init_portb (void){

PORTB = 0xff;DDRB = 0xff;

}

Note

Section .init3 is used in this example, as this ensures the inernal __zero_reg__ has already been set up. Thecode generated by the compiler might blindly rely on __zero_reg__ being really 0.

5 Data in Program Space

5.1 Introduction

So you have some constant data and you’re running out of room to store it? Many AVRs have limited amount of RAMin which to store data, but may have more Flash space available. The AVR is a Harvard architecture processor, where


5.2 A Note On const 23

Flash is used for the program, RAM is used for data, and they each have separate address spaces. It is a challenge toget constant data to be stored in the Program Space, and to retrieve that data to use it in the AVR application.

The problem is exacerbated by the fact that the C Language was not designed for Harvard architectures, it was designedfor Von Neumann architectures where code and data exist in the same address space. This means that any compilerfor a Harvard architecture processor, like the AVR, has to use other means to operate with separate address spaces.

Some compilers use non-standard C language keywords, or they extend the standard syntax in ways that are non-standard. The AVR toolset takes a different approach.

GCC has a special keyword, attribute that is used to attach different attributes to things such as function declara-tions, variables, and types. This keyword is followed by an attribute specification in double parentheses. In AVR GCC,there is a special attribute called progmem. This attribute is use on data declarations, and tells the compiler to placethe data in the Program Memory (Flash).

AVR-Libc provides a simple macro PROGMEM that is defined as the attribute syntax of GCC with the progmem attribute.This macro was created as a convenience to the end user, as we will see below. The PROGMEM macro is defined in the<avr/pgmspace.h> system header file.

It is difficult to modify GCC to create new extensions to the C language syntax, so instead, avr-libc has created macrosto retrieve the data from the Program Space. These macros are also found in the <avr/pgmspace.h> systemheader file.

5.2 A Note On const

Many users bring up the idea of using C’s keyword const as a means of declaring data to be in Program Space. Doingthis would be an abuse of the intended meaning of the const keyword.

const is used to tell the compiler that the data is to be "read-only". It is used to help make it easier for the compiler tomake certain transformations, or to help the compiler check for incorrect usage of those variables.

For example, the const keyword is commonly used in many functions as a modifier on the parameter type. This tellsthe compiler that the function will only use the parameter as read-only and will not modify the contents of the parametervariable.

const was intended for uses such as this, not as a means to identify where the data should be stored. If it were usedas a means to define data storage, then it loses its correct meaning (changes its semantics) in other situations such asin the function parameter example.

5.3 Storing and Retrieving Data in the Program Space

Let’s say you have some global data:

unsigned char mydata[11][10] ={

{0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09},{0x0A,0x0B,0x0C,0x0D,0x0E,0x0F,0x10,0x11,0x12,0x13},{0x14,0x15,0x16,0x17,0x18,0x19,0x1A,0x1B,0x1C,0x1D},{0x1E,0x1F,0x20,0x21,0x22,0x23,0x24,0x25,0x26,0x27},{0x28,0x29,0x2A,0x2B,0x2C,0x2D,0x2E,0x2F,0x30,0x31},{0x32,0x33,0x34,0x35,0x36,0x37,0x38,0x39,0x3A,0x3B},{0x3C,0x3D,0x3E,0x3F,0x40,0x41,0x42,0x43,0x44,0x45},{0x46,0x47,0x48,0x49,0x4A,0x4B,0x4C,0x4D,0x4E,0x4F},{0x50,0x51,0x52,0x53,0x54,0x55,0x56,0x57,0x58,0x59},{0x5A,0x5B,0x5C,0x5D,0x5E,0x5F,0x60,0x61,0x62,0x63},{0x64,0x65,0x66,0x67,0x68,0x69,0x6A,0x6B,0x6C,0x6D}

};

and later in your code you access this data in a function and store a single byte into a variable like so:

byte = mydata[i][j];


24 CONTENTS

Now you want to store your data in Program Memory. Use the PROGMEM macro found in <avr/pgmspace.h> andput it after the declaration of the variable, but before the initializer, like so:

#include <avr/pgmspace.h>...unsigned char mydata[11][10] PROGMEM ={

{0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09},{0x0A,0x0B,0x0C,0x0D,0x0E,0x0F,0x10,0x11,0x12,0x13},{0x14,0x15,0x16,0x17,0x18,0x19,0x1A,0x1B,0x1C,0x1D},{0x1E,0x1F,0x20,0x21,0x22,0x23,0x24,0x25,0x26,0x27},{0x28,0x29,0x2A,0x2B,0x2C,0x2D,0x2E,0x2F,0x30,0x31},{0x32,0x33,0x34,0x35,0x36,0x37,0x38,0x39,0x3A,0x3B},{0x3C,0x3D,0x3E,0x3F,0x40,0x41,0x42,0x43,0x44,0x45},{0x46,0x47,0x48,0x49,0x4A,0x4B,0x4C,0x4D,0x4E,0x4F},{0x50,0x51,0x52,0x53,0x54,0x55,0x56,0x57,0x58,0x59},{0x5A,0x5B,0x5C,0x5D,0x5E,0x5F,0x60,0x61,0x62,0x63},{0x64,0x65,0x66,0x67,0x68,0x69,0x6A,0x6B,0x6C,0x6D}

};

That’s it! Now your data is in the Program Space. You can compile, link, and check the map file to verify that mydatais placed in the correct section.

Now that your data resides in the Program Space, your code to access (read) the data will no longer work. The codethat gets generated will retrieve the data that is located at the address of the mydata array, plus offsets indexed by thei and j variables. However, the final address that is calculated where to the retrieve the data points to the Data Space!Not the Program Space where the data is actually located. It is likely that you will be retrieving some garbage. Theproblem is that AVR GCC does not intrinsically know that the data resides in the Program Space.

The solution is fairly simple. The "rule of thumb" for accessing data stored in the Program Space is to access the dataas you normally would (as if the variable is stored in Data Space), like so:

byte = mydata[i][j];

then take the address of the data:

byte = &(mydata[i][j]);

then use the appropriate pgm_read_∗ macro, and the address of your data becomes the parameter to that macro:

byte = pgm_read_byte(&(mydata[i][j]));

The pgm_read_∗ macros take an address that points to the Program Space, and retrieves the data that is storedat that address. This is why you take the address of the offset into the array. This address becomes the parameterto the macro so it can generate the correct code to retrieve the data from the Program Space. There are differentpgm_read_∗ macros to read different sizes of data at the address given.

5.4 Storing and Retrieving Strings in the Program Space

Now that you can successfully store and retrieve simple data from Program Space you want to store and retrive stringsfrom Program Space. And specifically you want to store and array of strings to Program Space. So you start off withyour array, like so:

char *string_table[] ={

"String 1","String 2","String 3","String 4","String 5"

};


5.4 Storing and Retrieving Strings in the Program Space 25

and then you add your PROGMEM macro to the end of the declaration:

char *string_table[] PROGMEM ={

"String 1","String 2","String 3","String 4","String 5"

};

Right? WRONG!

Unfortunately, with GCC attributes, they affect only the declaration that they are attached to. So in this case, wesuccessfully put the string_table variable, the array itself, in the Program Space. This DOES NOT put the actualstrings themselves into Program Space. At this point, the strings are still in the Data Space, which is probably not whatyou want.

In order to put the strings in Program Space, you have to have explicit declarations for each string, and put each stringin Program Space:

char string_1[] PROGMEM = "String 1";char string_2[] PROGMEM = "String 2";char string_3[] PROGMEM = "String 3";char string_4[] PROGMEM = "String 4";char string_5[] PROGMEM = "String 5";

Then use the new symbols in your table, like so:

PGM_P string_table[] PROGMEM ={

string_1,string_2,string_3,string_4,string_5

};

Now this has the effect of putting string_table in Program Space, where string_table is an array of pointersto characters (strings), where each pointer is a pointer to the Program Space, where each string is also stored.

The PGM_P type above is also a macro that defined as a pointer to a character in the Program Space.

Retrieving the strings are a different matter. You probably don’t want to pull the string out of Program Space, byte bybyte, using the pgm_read_byte() macro. There are other functions declared in the <avr/pgmspace.h> header filethat work with strings that are stored in the Program Space.

For example if you want to copy the string from Program Space to a buffer in RAM (like an automatic variable inside afunction, that is allocated on the stack), you can do this:

void foo(void){

char buffer[10];

for (unsigned char i = 0; i < 5; i++){

strcpy_P(buffer, (PGM_P)pgm_read_word(&(string_table[i])));

// Display buffer on LCD.}return;

}

Here, the string_table array is stored in Program Space, so we access it normally, as if were stored in Data Space,then take the address of the location we want to access, and use the address as a parameter to pgm_read_word.We use the pgm_read_word macro to read the string pointer out of the string_table array. Remember that


26 CONTENTS

a pointer is 16-bits, or word size. The pgm_read_word macro will return a 16-bit unsigned integer. We then haveto typecast it as a true pointer to program memory, PGM_P. This pointer is an address in Program Space pointing tothe string that we want to copy. This pointer is then used as a parameter to the function strcpy_P. The functionstrcpy_P is just like the regular strcpy function, except that it copies a string from Program Space (the secondparameter) to a buffer in the Data Space (the first parameter).

There are many string functions available that work with strings located in Program Space. All of these special stringfunctions have a suffix of _P in the function name, and are declared in the <avr/pgmspace.h> header file.

5.5 Caveats

The macros and functions used to retrieve data from the Program Space have to generate some extra code in order toactually load the data from the Program Space. This incurs some extra overhead in terms of code space (extra opcodes)and execution time. Usually, both the space and time overhead is minimal compared to the space savings of puttingdata in Program Space. But you should be aware of this so you can minimize the number of calls within a single functionthat gets the same piece of data from Program Space. It is always instructive to look at the resulting disassembly fromthe compiler.

6 avr-libc and assembler programs

6.1 Introduction

There might be several reasons to write code for AVR microcontrollers using plain assembler source code. Among themare:

• Code for devices that do not have RAM and are thus not supported by the C compiler.

• Code for very time-critical applications.

• Special tweaks that cannot be done in C.

Usually, all but the first could probably be done easily using the inline assembler facility of the compiler.

Although avr-libc is primarily targeted to support programming AVR microcontrollers using the C (and C++) language,there’s limited support for direct assembler usage as well. The benefits of it are:

• Use of the C preprocessor and thus the ability to use the same symbolic constants that are available to C pro-grams, as well as a flexible macro concept that can use any valid C identifier as a macro (whereas the assembler’smacro concept is basically targeted to use a macro in place of an assembler instruction).

• Use of the runtime framework like automatically assigning interrupt vectors. For devices that have RAM, initializingthe RAM variables can also be utilized.

6.2 Invoking the compiler

For the purpose described in this document, the assembler and linker are usually not invoked manually, but rather usingthe C compiler frontend (avr-gcc) that in turn will call the assembler and linker as required.

This approach has the following advantages:

• There is basically only one program to be called directly, avr-gcc, regardless of the actual source languageused.


6.3 Example program 27

• The invokation of the C preprocessor will be automatic, and will include the appropriate options to locate requiredinclude files in the filesystem.

• The invokation of the linker will be automatic, and will include the appropriate options to locate additional librariesas well as the application start-up code (crtXXX.o) and linker script.

Note that the invokation of the C preprocessor will be automatic when the filename provided for the assembler file endsin .S (the capital letter "s"). This would even apply to operating systems that use case-insensitive filesystems since theactual decision is made based on the case of the filename suffix given on the command-line, not based on the actualfilename from the file system.

As an alternative to using .S, the suffix .sx is recognized for this purpose (starting with GCC 4.3.0). This is primarilymeant to be compatible with other compiler environments that have been providing this variant before in order to copewith operating systems where filenames are case-insensitive (and, with some versions of make that could not distinguishbetween .s and .S on such systems).

Alternatively, the language can explicitly be specified using the -x assembler-with-cpp option.

6.3 Example program

The following annotated example features a simple 100 kHz square wave generator using an AT90S1200 clocked witha 10.7 MHz crystal. Pin PD6 will be used for the square wave output.

#include <avr/io.h> ; Note [1]

work = 16 ; Note [2]tmp = 17

inttmp = 19

intsav = 0

SQUARE = PD6 ; Note [3]

; Note [4]:tmconst= 10700000 / 200000 ; 100 kHz => 200000 edges/sfuzz= 8 ; # clocks in ISR until TCNT0 is set

.section .text

.global main ; Note [5]main:

rcall ioinit1:

rjmp 1b ; Note [6]

.global TIMER0_OVF_vect ; Note [7]TIMER0_OVF_vect:

ldi inttmp, 256 - tmconst + fuzzout _SFR_IO_ADDR(TCNT0), inttmp ; Note [8]

in intsav, _SFR_IO_ADDR(SREG) ; Note [9]

sbic _SFR_IO_ADDR(PORTD), SQUARErjmp 1fsbi _SFR_IO_ADDR(PORTD), SQUARErjmp 2f

1: cbi _SFR_IO_ADDR(PORTD), SQUARE2:

out _SFR_IO_ADDR(SREG), intsavreti

ioinit:sbi _SFR_IO_ADDR(DDRD), SQUARE

ldi work, _BV(TOIE0)out _SFR_IO_ADDR(TIMSK), work

ldi work, _BV(CS00) ; tmr0: CK/1


28 CONTENTS

out _SFR_IO_ADDR(TCCR0), work

ldi work, 256 - tmconstout _SFR_IO_ADDR(TCNT0), work

sei

ret

.global __vector_default ; Note [10]__vector_default:

reti

.end

Note [1]

As in C programs, this includes the central processor-specific file containing the IO port definitions for the device. Notethat not all include files can be included into assembler sources.

Note [2]

Assignment of registers to symbolic names used locally. Another option would be to use a C preprocessor macroinstead:

#define work 16

Note [3]

Our bit number for the square wave output. Note that the right-hand side consists of a CPP macro which will besubstituted by its value (6 in this case) before actually being passed to the assembler.

Note [4]

The assembler uses integer operations in the host-defined integer size (32 bits or longer) when evaluating expressions.This is in contrast to the C compiler that uses the C type int by default in order to calculate constant integer expres-sions.In order to get a 100 kHz output, we need to toggle the PD6 line 200000 times per second. Since we use timer 0without any prescaling options in order to get the desired frequency and accuracy, we already run into serious timingconsiderations: while accepting and processing the timer overflow interrupt, the timer already continues to count. Whenpre-loading the TCCNT0 register, we therefore have to account for the number of clock cycles required for interruptacknowledge and for the instructions to reload TCCNT0 (4 clock cycles for interrupt acknowledge, 2 cycles for the jumpfrom the interrupt vector, 2 cycles for the 2 instructions that reload TCCNT0). This is what the constant fuzz is for.

Note [5]

External functions need to be declared to be .global. main is the application entry point that will be jumped to from theininitalization routine in crts1200.o.


6.4 Pseudo-ops and operators 29

Note [6]

The main loop is just a single jump back to itself. Square wave generation itself is completely handled by the timer0 overflow interrupt service. A sleep instruction (using idle mode) could be used as well, but probably would notconserve much energy anyway since the interrupt service is executed quite frequently.

Note [7]

Interrupt functions can get the usual names that are also available to C programs. The linker will then put them into theappropriate interrupt vector slots. Note that they must be declared .global in order to be acceptable for this purpose.This will only work if <avr/io.h> has been included. Note that the assembler or linker have no chance to check thecorrect spelling of an interrupt function, so it should be double-checked. (When analyzing the resulting object file usingavr-objdump or avr-nm, a name like __vector_N should appear, with N being a small integer number.)

Note [8]

As explained in the section about special function registers, the actual IO port address should be obtained using themacro _SFR_IO_ADDR. (The AT90S1200 does not have RAM thus the memory-mapped approach to access the IOregisters is not available. It would be slower than using in / out instructions anyway.)Since the operation to reload TCCNT0 is time-critical, it is even performed before saving SREG. Obviously, this requiresthat the instructions involved would not change any of the flag bits in SREG.

Note [9]

Interrupt routines must not clobber the global CPU state. Thus, it is usually necessary to save at least the state of theflag bits in SREG. (Note that this serves as an example here only since actually, all the following instructions would notmodify SREG either, but that’s not commonly the case.)Also, it must be made sure that registers used inside the interrupt routine do not conflict with those used outside. Inthe case of a RAM-less device like the AT90S1200, this can only be done by agreeing on a set of registers to be usedexclusively inside the interrupt routine; there would not be any other chance to "save" a register anywhere.If the interrupt routine is to be linked together with C modules, care must be taken to follow the register usage guidelinesimposed by the C compiler. Also, any register modified inside the interrupt sevice needs to be saved, usually on thestack.

Note [10]

As explained in Interrupts, a global "catch-all" interrupt handler that gets all unassigned interrupt vectors can be installedusing the name __vector_default. This must be .global, and obviously, should end in a reti instruction. (Bydefault, a jump to location 0 would be implied instead.)

6.4 Pseudo-ops and operators

The available pseudo-ops in the assembler are described in the GNU assembler (gas) manual. The manual can befound online as part of the current binutils release under http://sources.redhat.com/binutils/.


http://sources.redhat.com/binutils/

30 CONTENTS

As gas comes from a Unix origin, its pseudo-op and overall assembler syntax is slightly different than the one beingused by other assemblers. Numeric constants follow the C notation (prefix 0x for hexadecimal constants), expressionsuse a C-like syntax.

Some common pseudo-ops include:

• .byte allocates single byte constants

• .ascii allocates a non-terminated string of characters

• .asciz allocates a \0-terminated string of characters (C string)

• .data switches to the .data section (initialized RAM variables)

• .text switches to the .text section (code and ROM constants)

• .set declares a symbol as a constant expression (identical to .equ)

• .global (or .globl) declares a public symbol that is visible to the linker (e. g. function entry point, global variable)

• .extern declares a symbol to be externally defined; this is effectively a comment only, as gas treats all undefinedsymbols it encounters as globally undefined anyway

Note that .org is available in gas as well, but is a fairly pointless pseudo-op in an assembler environment that usesrelocatable object files, as it is the linker that determines the final position of some object in ROM or RAM.

Along with the architecture-independent standard operators, there are some AVR-specific operators available which areunfortunately not yet described in the official documentation. The most notable operators are:

• lo8 Takes the least significant 8 bits of a 16-bit integer

• hi8 Takes the most significant 8 bits of a 16-bit integer

• pm Takes a program-memory (ROM) address, and converts it into a RAM address. This implies a division by 2 asthe AVR handles ROM addresses as 16-bit words (e.g. in an IJMP or ICALL instruction), and can also handlerelocatable symbols on the right-hand side.

Example:

ldi r24, lo8(pm(somefunc))ldi r25, hi8(pm(somefunc))call something

This passes the address of function somefunc as the first parameter to function something.

7 Inline Assembler Cookbook

AVR-GCCInline Assembler Cookbook

About this Document

The GNU C compiler for Atmel AVR RISC processors offers, to embed assembly language code into C programs.This cool feature may be used for manually optimizing time critical parts of the software or to use specific processorinstruction, which are not available in the C language.

Because of a lack of documentation, especially for the AVR version of the compiler, it may take some time to figure outthe implementation details by studying the compiler and assembler source code. There are also a few sample programsavailable in the net. Hopefully this document will help to increase their number.


7.1 GCC asm Statement 31

It’s assumed, that you are familiar with writing AVR assembler programs, because this is not an AVR assembler pro-gramming tutorial. It’s not a C language tutorial either.

Note that this document does not cover file written completely in assembler language, refer to avr-libc and assemblerprograms for this.

Copyright (C) 2001-2002 by egnite Software GmbH

Permission is granted to copy and distribute verbatim copies of this manual provided that the copyright notice and thispermission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of thismanual provided that the entire resulting derived work is distributed under the terms of a permission notice identical tothis one.

This document describes version 3.3 of the compiler. There may be some parts, which hadn’t been completely un-derstood by the author himself and not all samples had been tested so far. Because the author is German and notfamiliar with the English language, there are definitely some typos and syntax errors in the text. As a programmer theauthor knows, that a wrong documentation sometimes might be worse than none. Anyway, he decided to offer his littleknowledge to the public, in the hope to get enough response to improve this document. Feel free to contact the authorvia e-mail. For the latest release check http://www.ethernut.de/.

Herne, 17th of May 2002 Harald Kipp harald.kipp-at-egnite.de

Note

As of 26th of July 2002, this document has been merged into the documentation for avr-libc. The latest version isnow available at http://savannah.nongnu.org/projects/avr-libc/.

7.1 GCC asm Statement

Let’s start with a simple example of reading a value from port D:

asm("in %0, %1" : "=r" (value) : "I" (_SFR_IO_ADDR(PORTD)) );

Each asm statement is devided by colons into (up to) four parts:

1. The assembler instructions, defined as a single string constant:

"in %0, %1"

2. A list of output operands, separated by commas. Our example uses just one:

"=r" (value)

3. A comma separated list of input operands. Again our example uses one operand only:

"I" (_SFR_IO_ADDR(PORTD))

4. Clobbered registers, left empty in our example.

You can write assembler instructions in much the same way as you would write assembler programs. However, registersand constants are used in a different way if they refer to expressions of your C program. The connection betweenregisters and C operands is specified in the second and third part of the asm instruction, the list of input and outputoperands, respectively. The general form is

asm(code : output operand list : input operand list [: clobber list]);


http://www.ethernut.de/

http://savannah.nongnu.org/projects/avr-libc/

32 CONTENTS

In the code section, operands are referenced by a percent sign followed by a single digit. %0 refers to the first %1 to thesecond operand and so forth. From the above example:

%0 refers to "=r" (value) and%1 refers to "I" (_SFR_IO_ADDR(PORTD)).

This may still look a little odd now, but the syntax of an operand list will be explained soon. Let us first examine the partof a compiler listing which may have been generated from our example:

lds r24,value/* #APP */

in r24, 12/* #NOAPP */

sts value,r24

The comments have been added by the compiler to inform the assembler that the included code was not generated bythe compilation of C statements, but by inline assembler statements. The compiler selected register r24 for storageof the value read from PORTD. The compiler could have selected any other register, though. It may not explicitely loador store the value and it may even decide not to include your assembler code at all. All these decisions are part of thecompiler’s optimization strategy. For example, if you never use the variable value in the remaining part of the C program,the compiler will most likely remove your code unless you switched off optimization. To avoid this, you can add thevolatile attribute to the asm statement:

asm volatile("in %0, %1" : "=r" (value) : "I" (_SFR_IO_ADDR(PORTD)));

Alternatively, operands can be given names. The name is prepended in brackets to the constraints in the operand list,and references to the named operand use the bracketed name instead of a number after the % sign. Thus, the aboveexample could also be written as

asm("in %[retval], %[port]" :[retval] "=r" (value) :[port] "I" (_SFR_IO_ADDR(PORTD)) );

The last part of the asm instruction, the clobber list, is mainly used to tell the compiler about modifications done by theassembler code. This part may be omitted, all other parts are required, but may be left empty. If your assembler routinewon’t use any input or output operand, two colons must still follow the assembler code string. A good example is asimple statement to disable interrupts:

asm volatile("cli"::);

7.2 Assembler Code

You can use the same assembler instruction mnemonics as you’d use with any other AVR assembler. And you can writeas many assembler statements into one code string as you like and your flash memory is able to hold.

Note

The available assembler directives vary from one assembler to another.

To make it more readable, you should put each statement on a seperate line:

asm volatile("nop\n\t""nop\n\t""nop\n\t""nop\n\t"::);

The linefeed and tab characters will make the assembler listing generated by the compiler more readable. It may look abit odd for the first time, but that’s the way the compiler creates it’s own assembler code.

You may also make use of some special registers.


7.3 Input and Output Operands 33

Symbol Register__SREG__ Status register at address 0x3F__SP_H__ Stack pointer high byte at address 0x3E__SP_L__ Stack pointer low byte at address 0x3D__tmp_reg__ Register r0, used for temporary storage__zero_reg__ Register r1, always zero

Register r0 may be freely used by your assembler code and need not be restored at the end of your code. It’s a goodidea to use tmp_reg and zero_reg instead of r0 or r1, just in case a new compiler version changes the registerusage definitions.

7.3 Input and Output Operands

Each input and output operand is described by a constraint string followed by a C expression in parantheses. AVR-GCC3.3 knows the following constraint characters:

Note

The most up-to-date and detailed information on contraints for the avr can be found in the gcc manual.The x register is r27:r26, the y register is r29:r28, and the z register is r31:r30

Constraint Used for Rangea Simple upper registers r16 to r23b Base pointer registers pairs y, zd Upper register r16 to r31e Pointer register pairs x, y, zq Stack pointer register SPH:SPLr Any register r0 to r31t Temporary register r0w Special upper register pairs r24, r26, r28, r30x Pointer register pair X x (r27:r26)y Pointer register pair Y y (r29:r28)z Pointer register pair Z z (r31:r30)G Floating point constant 0.0I 6-bit positive integer constant 0 to 63J 6-bit negative integer constant -63 to 0K Integer constant 2L Integer constant 0l Lower registers r0 to r15M 8-bit integer constant 0 to 255N Integer constant -1O Integer constant 8, 16, 24P Integer constant 1Q (GCC >= 4.2.x) A memory address

based on Y or Z pointer withdisplacement.


34 CONTENTS

R (GCC >= 4.3.x) Integer constant. -6 to 5

The selection of the proper contraint depends on the range of the constants or registers, which must be acceptable tothe AVR instruction they are used with. The C compiler doesn’t check any line of your assembler code. But it is able tocheck the constraint against your C expression. However, if you specify the wrong constraints, then the compiler maysilently pass wrong code to the assembler. And, of course, the assembler will fail with some cryptic output or internalerrors. For example, if you specify the constraint "r" and you are using this register with an "ori" instruction in yourassembler code, then the compiler may select any register. This will fail, if the compiler chooses r2 to r15. (It will neverchoose r0 or r1, because these are uses for special purposes.) That’s why the correct constraint in that case is "d".On the other hand, if you use the constraint "M", the compiler will make sure that you don’t pass anything else but an8-bit value. Later on we will see how to pass multibyte expression results to the assembler code.

The following table shows all AVR assembler mnemonics which require operands, and the related contraints. Becauseof the improper constraint definitions in version 3.3, they aren’t strict enough. There is, for example, no constraint, whichrestricts integer constants to the range 0 to 7 for bit set and bit clear operations.

Mnemonic Constraints Mnemonic Constraintsadc r,r add r,radiw w,I and r,randi d,M asr rbclr I bld r,Ibrbc I,label brbs I,labelbset I bst r,Icbi I,I cbr d,Icom r cp r,rcpc r,r cpi d,Mcpse r,r dec relpm t,z eor r,rin r,I inc rld r,e ldd r,bldi d,M lds r,labellpm t,z lsl rlsr r mov r,rmovw r,r mul r,rneg r or r,rori d,M out I,rpop r push rrol r ror rsbc r,r sbci d,Msbi I,I sbic I,Isbiw w,I sbr d,Msbrc r,I sbrs r,Iser d st e,rstd b,r sts label,rsub r,r subi d,Mswap r

Constraint characters may be prepended by a single constraint modifier. Contraints without a modifier specify read-onlyoperands. Modifiers are:

Modifier Specifies= Write-only operand, usually used for all output

operands.


7.3 Input and Output Operands 35

+ Read-write operand& Register should be used for output only

Output operands must be write-only and the C expression result must be an lvalue, which means that the operandsmust be valid on the left side of assignments. Note, that the compiler will not check if the operands are of reasonabletype for the kind of operation used in the assembler instructions.

Input operands are, you guessed it, read-only. But what if you need the same operand for input and output? As statedabove, read-write operands are not supported in inline assembler code. But there is another solution. For input operatorsit is possible to use a single digit in the constraint string. Using digit n tells the compiler to use the same register as forthe n-th operand, starting with zero. Here is an example:

asm volatile("swap %0" : "=r" (value) : "0" (value));

This statement will swap the nibbles of an 8-bit variable named value. Constraint "0" tells the compiler, to use thesame input register as for the first operand. Note however, that this doesn’t automatically imply the reverse case. Thecompiler may choose the same registers for input and output, even if not told to do so. This is not a problem in mostcases, but may be fatal if the output operator is modified by the assembler code before the input operator is used. Inthe situation where your code depends on different registers used for input and output operands, you must add the &constraint modifier to your output operand. The following example demonstrates this problem:

asm volatile("in %0,%1" "\n\t""out %1, %2" "\n\t": "=&r" (input): "I" (_SFR_IO_ADDR(port)), "r" (output));

In this example an input value is read from a port and then an output value is written to the same port. If the compilerwould have choosen the same register for input and output, then the output value would have been destroyed on thefirst assembler instruction. Fortunately, this example uses the & constraint modifier to instruct the compiler not to selectany register for the output value, which is used for any of the input operands. Back to swapping. Here is the code toswap high and low byte of a 16-bit value:

asm volatile("mov __tmp_reg__, %A0" "\n\t""mov %A0, %B0" "\n\t""mov %B0, __tmp_reg__" "\n\t": "=r" (value): "0" (value));

First you will notice the usage of register __tmp_reg__, which we listed among other special registers in the Assem-bler Code section. You can use this register without saving its contents. Completely new are those letters A and B in%A0 and %B0. In fact they refer to two different 8-bit registers, both containing a part of value.

Another example to swap bytes of a 32-bit value:

asm volatile("mov __tmp_reg__, %A0" "\n\t""mov %A0, %D0" "\n\t""mov %D0, __tmp_reg__" "\n\t""mov __tmp_reg__, %B0" "\n\t""mov %B0, %C0" "\n\t""mov %C0, __tmp_reg__" "\n\t": "=r" (value): "0" (value));

Instead of listing the same operand as both, input and output operand, it can also be declared as a read-write operand.This must be applied to an output operand, and the respective input operand list remains empty:

asm volatile("mov __tmp_reg__, %A0" "\n\t""mov %A0, %D0" "\n\t""mov %D0, __tmp_reg__" "\n\t"


36 CONTENTS

"mov __tmp_reg__, %B0" "\n\t""mov %B0, %C0" "\n\t""mov %C0, __tmp_reg__" "\n\t": "+r" (value));

If operands do not fit into a single register, the compiler will automatically assign enough registers to hold the entireoperand. In the assembler code you use %A0 to refer to the lowest byte of the first operand, %A1 to the lowest byte ofthe second operand and so on. The next byte of the first operand will be %B0, the next byte %C0 and so on.

This also implies, that it is often neccessary to cast the type of an input operand to the desired size.

A final problem may arise while using pointer register pairs. If you define an input operand

"e" (ptr)

and the compiler selects register Z (r30:r31), then

%A0 refers to r30 and%B0 refers to r31.

But both versions will fail during the assembly stage of the compiler, if you explicitely need Z, like in

ld r24,Z

If you write

ld r24, %a0

with a lower case a following the percent sign, then the compiler will create the proper assembler line.

7.4 Clobbers

As stated previously, the last part of the asm statement, the list of clobbers, may be omitted, including the colonseperator. However, if you are using registers, which had not been passed as operands, you need to inform the compilerabout this. The following example will do an atomic increment. It increments an 8-bit value pointed to by a pointer variablein one go, without being interrupted by an interrupt routine or another thread in a multithreaded environment. Note, thatwe must use a pointer, because the incremented value needs to be stored before interrupts are enabled.

asm volatile("cli" "\n\t""ld r24, %a0" "\n\t""inc r24" "\n\t""st %a0, r24" "\n\t""sei" "\n\t":: "e" (ptr): "r24"

);

The compiler might produce the following code:

clild r24, Zinc r24st Z, r24sei

One easy solution to avoid clobbering register r24 is, to make use of the special temporary register tmp_reg definedby the compiler.


7.4 Clobbers 37

asm volatile("cli" "\n\t""ld __tmp_reg__, %a0" "\n\t""inc __tmp_reg__" "\n\t""st %a0, __tmp_reg__" "\n\t""sei" "\n\t":: "e" (ptr)

);

The compiler is prepared to reload this register next time it uses it. Another problem with the above code is, that itshould not be called in code sections, where interrupts are disabled and should be kept disabled, because it will enableinterrupts at the end. We may store the current status, but then we need another register. Again we can solve thiswithout clobbering a fixed, but let the compiler select it. This could be done with the help of a local C variable.

{uint8_t s;asm volatile(

"in %0, __SREG__" "\n\t""cli" "\n\t""ld __tmp_reg__, %a1" "\n\t""inc __tmp_reg__" "\n\t""st %a1, __tmp_reg__" "\n\t""out __SREG__, %0" "\n\t": "=&r" (s): "e" (ptr)

);}

Now every thing seems correct, but it isn’t really. The assembler code modifies the variable, that ptr points to. Thecompiler will not recognize this and may keep its value in any of the other registers. Not only does the compiler work withthe wrong value, but the assembler code does too. The C program may have modified the value too, but the compilerdidn’t update the memory location for optimization reasons. The worst thing you can do in this case is:

{uint8_t s;asm volatile(

"in %0, __SREG__" "\n\t""cli" "\n\t""ld __tmp_reg__, %a1" "\n\t""inc __tmp_reg__" "\n\t""st %a1, __tmp_reg__" "\n\t""out __SREG__, %0" "\n\t": "=&r" (s): "e" (ptr): "memory"

);}

The special clobber "memory" informs the compiler that the assembler code may modify any memory location. It forcesthe compiler to update all variables for which the contents are currently held in a register before executing the assemblercode. And of course, everything has to be reloaded again after this code.

In most situations, a much better solution would be to declare the pointer destination itself volatile:

volatile uint8_t *ptr;

This way, the compiler expects the value pointed to by ptr to be changed and will load it whenever used and store itwhenever modified.

Situations in which you need clobbers are very rare. In most cases there will be better ways. Clobbered registers willforce the compiler to store their values before and reload them after your assembler code. Avoiding clobbers gives thecompiler more freedom while optimizing your code.


38 CONTENTS

7.5 Assembler Macros

In order to reuse your assembler language parts, it is useful to define them as macros and put them into include files.AVR Libc comes with a bunch of them, which could be found in the directory avr/include. Using such include filesmay produce compiler warnings, if they are used in modules, which are compiled in strict ANSI mode. To avoid that, youcan write asm instead of asm and volatile instead of volatile. These are equivalent aliases.

Another problem with reused macros arises if you are using labels. In such cases you may make use of the specialpattern %=, which is replaced by a unique number on each asm statement. The following code had been taken fromavr/include/iomacros.h:

#define loop_until_bit_is_clear(port,bit) \__asm__ __volatile__ ( \"L_%=: " "sbic %0, %1" "\n\t" \

"rjmp L_%=" \: /* no outputs */: "I" (_SFR_IO_ADDR(port)),"I" (bit)

)

When used for the first time, L_%= may be translated to L_1404, the next usage might create L_1405 or whatever.In any case, the labels became unique too.

Another option is to use Unix-assembler style numeric labels. They are explained in How do I trace an assembler file inavr-gdb?. The above example would then look like:

#define loop_until_bit_is_clear(port,bit)__asm__ __volatile__ ("1: " "sbic %0, %1" "\n\t"

"rjmp 1b": /* no outputs */: "I" (_SFR_IO_ADDR(port)),"I" (bit)

)

7.6 C Stub Functions

Macro definitions will include the same assembler code whenever they are referenced. This may not be acceptable forlarger routines. In this case you may define a C stub function, containing nothing other than your assembler code.

void delay(uint8_t ms){

uint16_t cnt;asm volatile (

"\n""L_dl1%=:" "\n\t""mov %A0, %A2" "\n\t""mov %B0, %B2" "\n""L_dl2%=:" "\n\t""sbiw %A0, 1" "\n\t""brne L_dl2%=" "\n\t""dec %1" "\n\t""brne L_dl1%=" "\n\t": "=&w" (cnt): "r" (ms), "r" (delay_count));

}

The purpose of this function is to delay the program execution by a specified number of milliseconds using a countingloop. The global 16 bit variable delay_count must contain the CPU clock frequency in Hertz divided by 4000 and musthave been set before calling this routine for the first time. As described in the clobber section, the routine uses a localvariable to hold a temporary value.


7.7 C Names Used in Assembler Code 39

Another use for a local variable is a return value. The following function returns a 16 bit value read from two successiveport addresses.

uint16_t inw(uint8_t port){

uint16_t result;asm volatile (

"in %A0,%1" "\n\t""in %B0,(%1) + 1": "=r" (result): "I" (_SFR_IO_ADDR(port)));

return result;}

Note

inw() is supplied by avr-libc.

7.7 C Names Used in Assembler Code

By default AVR-GCC uses the same symbolic names of functions or variables in C and assembler code. You can specifya different name for the assembler code by using a special form of the asm statement:

unsigned long value asm("clock") = 3686400;

This statement instructs the compiler to use the symbol name clock rather than value. This makes sense only forexternal or static variables, because local variables do not have symbolic names in the assembler code. However, localvariables may be held in registers.

With AVR-GCC you can specify the use of a specific register:

void Count(void){

register unsigned char counter asm("r3");

... some code...asm volatile("clr r3");... more code...

}

The assembler instruction, "clr r3", will clear the variable counter. AVR-GCC will not completely reserve the speci-fied register. If the optimizer recognizes that the variable will not be referenced any longer, the register may be re-used.But the compiler is not able to check wether this register usage conflicts with any predefined register. If you reserve toomany registers in this way, the compiler may even run out of registers during code generation.

In order to change the name of a function, you need a prototype declaration, because the compiler will not accept theasm keyword in the function definition:

extern long Calc(void) asm ("CALCULATE");

Calling the function Calc() will create assembler instructions to call the function CALCULATE.

7.8 Links

For a more thorough discussion of inline assembly usage, see the gcc user manual. The latest version of the gcc manualis always available here: http://gcc.gnu.org/onlinedocs/


http://gcc.gnu.org/onlinedocs/

40 CONTENTS

8 How to Build a Library

8.1 Introduction

So you keep reusing the same functions that you created over and over? Tired of cut and paste going from one projectto the next? Would you like to reduce your maintenance overhead? Then you’re ready to create your own library!Code reuse is a very laudable goal. With some upfront investment, you can save time and energy on future projects byhaving ready-to-go libraries. This chapter describes some background information, design considerations, and practicalknowledge that you will need to create and use your own libraries.

8.2 How the Linker Works

The compiler compiles a single high-level language file (C language, for example) into a single object module file. Thelinker (ld) can only work with object modules to link them together. Object modules are the smallest unit that the linkerworks with.

Typically, on the linker command line, you will specify a set of object modules (that has been previously compiled) andthen a list of libraries, including the Standard C Library. The linker takes the set of object modules that you specify on thecommand line and links them together. Afterwards there will probably be a set of "undefined references". A reference isessentially a function call. An undefined reference is a function call, with no defined function to match the call.

The linker will then go through the libraries, in order, to match the undefined references with function definitions that arefound in the libraries. If it finds the function that matches the call, the linker will then link in the object module in whichthe function is located. This part is important: the linker links in THE ENTIRE OBJECT MODULE in which the functionis located. Remember, the linker knows nothing about the functions internal to an object module, other than symbolnames (such as function names). The smallest unit the linker works with is object modules.

When there are no more undefined references, the linker has linked everything and is done and outputs the finalapplication.

8.3 How to Design a Library

How the linker behaves is very important in designing a library. Ideally, you want to design a library where only thefunctions that are called are the only functions to be linked into the final application. This helps keep the code size toa minimum. In order to do this, with the way the linker works, is to only write one function per code module. This willcompile to one function per object module. This is usually a very different way of doing things than writing an application!

There are always exceptions to the rule. There are generally two cases where you would want to have more than onefunction per object module.

The first is when you have very complementary functions that it doesn’t make much sense to split them up. For example,malloc() and free(). If someone is going to use malloc(), they will very likely be using free() (or at least should be usingfree()). In this case, it makes more sense to aggregate those two functions in the same object module.

The second case is when you want to have an Interrupt Service Routine (ISR) in your library that you want to link in. Theproblem in this case is that the linker looks for unresolved references and tries to resolve them with code in libraries. Areference is the same as a function call. But with ISRs, there is no function call to initiate the ISR. The ISR is placed inthe Interrupt Vector Table (IVT), hence no call, no reference, and no linking in of the ISR. In order to do this, you have totrick the linker in a way. Aggregate the ISR, with another function in the same object module, but have the other functionbe something that is required for the user to call in order to use the ISR, like perhaps an initialization function for thesubsystem, or perhaps a function that enables the ISR in the first place.


8.4 Creating a Library 41

8.4 Creating a Library

The librarian program is called ar (for "archiver") and is found in the GNU Binutils project. This program will have beenbuilt for the AVR target and will therefore be named avr-ar.

The job of the librarian program is simple: aggregate a list of object modules into a single library (archive) and create anindex for the linker to use. The name that you create for the library filename must follow a specific pattern: libname.a.The name part is the unique part of the filename that you create. It makes it easier if the name part relates to whatthe library is about. This name part must be prefixed by "lib", and it must have a file extension of .a, for "archive". Thereason for the special form of the filename is for how the library gets used by the toolchain, as we will see later on.

Note

The filename is case-sensitive. Use a lowercase "lib" prefix, and a lowercase ".a" as the file extension.

The command line is fairly simple:

avr-ar rcs <library name> <list of object modules>

The r command switch tells the program to insert the object modules into the archive with replacement. The c commandline switch tells the program to create the archive. And the s command line switch tells the program to write an object-fileindex into the archive, or update an existing one. This last switch is very important as it helps the linker to find what itneeds to do its job.

Note

The command line switches are case sensitive! There are uppercase switches that have completely differentactions.MFile and the WinAVR distribution contain a Makefile Template that includes the necessary command lines to builda library. You will have to manually modify the template to switch it over to build a library instead of an application.

See the GNU Binutils manual for more information on the ar program.

8.5 Using a Library

To use a library, use the -l switch on your linker command line. The string immediately following the -l is the uniquepart of the library filename that the linker will link in. For example, if you use:

-lm

this will expand to the library filename:

libm.a

which happens to be the math library included in avr-libc.

If you use this on your linker command line:

-lprintf_flt

then the linker will look for a library called:

libprintf_flt.a


42 CONTENTS

This is why naming your library is so important when you create it!

The linker will search libraries in the order that they appear on the command line. Whichever function is found first thatmatches the undefined reference, it will be linked in.

There are also command line switches that tell GCC which directory to look in (-L) for the libraries that are specified tobe linke in with -l.

See the GNU Binutils manual for more information on the GNU linker (ld) program.

9 Benchmarks

The results below can only give a rough estimate of the resources necessary for using certain library functions. Thereis a number of factors which can both increase or reduce the effort required:

• Expenses for preparation of operands and their stack are not considered.

• In the table, the size includes all additional functions (for example, function to multiply two integers) but they areonly linked from the library.

• Expenses of time of performance of some functions essentially depend on parameters of a call, for example,qsort() is recursive, and sprintf() receives parameters in a stack.

• Different versions of the compiler can give a significant difference in code size and execution time. For example,the dtostre() function, compiled with avr-gcc 3.4.6, requires 930 bytes. After transition to avr-gcc 4.2.3, the sizebecome 1088 bytes.

9.1 A few of libc functions.

Avr-gcc version is 4.7.1

The size of function is given in view of all picked up functions. By default Avr-libc is compiled with-mcall-prologues option. In brackets the size without taking into account modules of a prologue and anepilogue is resulted. Both of the size can coincide, if function does not cause a prologue/epilogue.

Function Units Avr2 Avr25 Avr4atoi ("12345") Flash bytes

Stack bytesMCU clocks

82 (82)2155

78 (78)2149

74 (74)2149

atol ("12345") Flash bytesStack bytesMCU clocks

122 (122)2221

118 (118)2219

118 (118)2219

dtostre (1.2345, s, 6, 0) Flash bytesStack bytesMCU clocks

1116 (1004)171247

1048 (938)171105

1048 (938)171105

dtostrf (1.2345, 15, 6, s) Flash bytesStack bytesMCU clocks

1616 (1616)381634

1508 (1508)381462

1508 (1508)381462

itoa (12345, s, 10) Flash bytesStack bytesMCU clocks

110 (110)2879

102 (102)2875

102 (102)2875


9.2 Math functions. 43

ltoa (12345L, s, 10) Flash bytesStack bytesMCU clocks

134 (134)21597

126 (126)21593

126 (126)21593

malloc (1) Flash bytesStack bytesMCU clocks

768 (712)6215

714 (660)6201

714 (660)6201

realloc ((void ∗)0, 1) Flash bytesStack bytesMCU clocks

1284 (1172)18305

1174 (1064)18286

1174 (1064)18286

qsort (s, sizeof(s), 1,cmp)

Flash bytesStack bytesMCU clocks

1252 (1140)4221996

1022 (912)4219905

1028 (918)4217541

sprintf_min (s, "%d",12345)


1224 (1112)531841

1092 (982)531694

1088 (978)531689

sprintf (s, "%d", 12345) Flash bytesStack bytesMCU clocks

1614 (1502)581647

1476 (1366)581552

1454 (1344)581547

sprintf_flt (s, "%e",1.2345)


3228 (3116)672573

2990 (2880)672311

2968 (2858)672311

sscanf_min ("12345","%d", &i)


1532 (1420)551607

1328 (1218)551446

1328 (1218)551446

sscanf ("12345", "%d",&i)


2008 (1896)551610

1748 (1638)551449

1748 (1638)551449

sscanf ("point,color","%[a-z]", s)


2008 (1896)863067

1748 (1638)862806

1748 (1638)862806

sscanf_flt ("1.2345","%e", &x)


3464 (3352)712497

3086 (2976)712281

3070 (2960)712078

strtod ("1.2345", &p) Flash bytesStack bytesMCU clocks

1632 (1520)201235

1536 (1426)201177

1480 (1480)211124

strtol ("12345", &p, 0) Flash bytesStack bytesMCU clocks

918 (806)22956

834 (724)22891

792 (792)28794

9.2 Math functions.

The table contains the number of MCU clocks to calculate a function with a given argument(s). The main reason of abig difference between Avr2 and Avr4 is a hardware multiplication.

Function Avr2 Avr4__addsf3 (1.234, 5.678) 113 108__mulsf3 (1.234, 5.678) 375 138__divsf3 (1.234, 5.678) 466 465acos (0.54321) 4411 2455asin (0.54321) 4517 2556atan (0.54321) 4710 2271atan2 (1.234, 5.678) 5270 2857cbrt (1.2345) 2684 2555ceil (1.2345) 177 177cos (1.2345) 3387 1671cosh (1.2345) 4922 2979


44 CONTENTS

exp (1.2345) 4708 2765fdim (5.678, 1.234) 111 111floor (1.2345) 180 180fmax (1.234, 5.678) 39 37fmin (1.234, 5.678) 35 35fmod (5.678, 1.234) 131 131frexp (1.2345, 0) 42 41hypot (1.234, 5.678) 1341 866ldexp (1.2345, 6) 42 42log (1.2345) 4142 2134log10 (1.2345) 4498 2260modf (1.2345, 0) 433 429pow (1.234, 5.678) 9293 5047round (1.2345) 150 150sin (1.2345) 3353 1653sinh (1.2345) 4946 3003sqrt (1.2345) 494 492tan (1.2345) 4381 2426tanh (1.2345) 5126 3173trunc (1.2345) 178 178

10 Porting From IAR to AVR GCC

10.1 Introduction

C language was designed to be a portable language. There two main types of porting activities: porting an applicationto a different platform (OS and/or processor), and porting to a different compiler. Porting to a different compiler can beexacerbated when the application is an embedded system. For example, the C language Standard, strangely, does notspecify a standard for declaring and defining Interrupt Service Routines (ISRs). Different compilers have different waysof defining registers, some of which use non-standard language constructs.

This chapter describes some methods and pointers on porting an AVR application built with the IAR compiler to theGNU toolchain (AVR GCC). Note that this may not be an exhaustive list.

10.2 Registers

IO header files contain identifiers for all the register names and bit names for a particular processor. IAR has individualheader files for each processor and they must be included when registers are being used in the code. For example:

#include <iom169.h>

Note

IAR does not always use the same register names or bit names that are used in the AVR datasheet.

AVR GCC also has individual IO header files for each processor. However, the actual processor type is specified as acommand line flag to the compiler. (Using the -mmcu=processor flag.) This is usually done in the Makefile. Thisallows you to specify only a single header file for any processor type:

#include <avr/io.h>


10.3 Interrupt Service Routines (ISRs) 45

Note

The forward slash in the <avr/io.h> file name that is used to separate subdirectories can be used on Windowsdistributions of the toolchain and is the recommended method of including this file.

The compiler knows the processor type and through the single header file above, it can pull in and include the correctindividual IO header file. This has the advantage that you only have to specify one generic header file, and you caneasily port your application to another processor type without having to change every file to include the new IO headerfile.

The AVR toolchain tries to adhere to the exact names of the registers and names of the bits found in the AVR datasheet.There may be some descrepencies between the register names found in the IAR IO header files and the AVR GCC IOheader files.

10.3 Interrupt Service Routines (ISRs)

As mentioned above, the C language Standard, strangely, does not specify a standard way of declaring and defining anISR. Hence, every compiler seems to have their own special way of doing so.

IAR declares an ISR like so:

#pragma vector=TIMER0_OVF_vect__interrupt void MotorPWMBottom(){

// code}

In AVR GCC, you declare an ISR like so:

ISR(PCINT1_vect){

//code}

AVR GCC uses the ISR macro to define an ISR. This macro requries the header file:

#include <avr/interrupt.h>

The names of the various interrupt vectors are found in the individual processor IO header files that you must includewith <avr/io.h>.

Note

The names of the interrupt vectors in AVR GCC has been changed to match the names of the vectors in IAR. Thissignificantly helps in porting applications from IAR to AVR GCC.

10.4 Intrinsic Routines

IAR has a number of intrinsic routine such as

__enable_interrupts() __disable_interrupts() __watchdog_reset()

These intrinsic functions compile to specific AVR opcodes (SEI, CLI, WDR).

There are equivalent macros that are used in AVR GCC, however they are not located in a single include file.

AVR GCC has sei() for __enable_interrupts(), and cli() for __disable_interrupts(). Both ofthese macros are located in <avr/interrupts.h>.

AVR GCC has the macro wdt_reset() in place of __watchdog_reset(). However, there is a whole WatchdogTimer API available in AVR GCC that can be found in <avr/wdt.h>.


46 CONTENTS

10.5 Flash Variables

The C language was not designed for Harvard architecture processors with separate memory spaces. This means thatthere are various non-standard ways to define a variable whose data resides in the Program Memory (Flash).

IAR uses a non-standard keyword to declare a variable in Program Memory:

__flash int mydata[] = ....

AVR GCC uses Variable Attributes to achieve the same effect:

int mydata[] __attribute__((progmem))

Note

See the GCC User Manual for more information about Variable Attributes.

avr-libc provides a convenience macro for the Variable Attribute:

#include <avr/pgmspace.h>...int mydata[] PROGMEM = ....

Note

The PROGMEM macro expands to the Variable Attribute of progmem. This macro requires that you include<avr/pgmspace.h>. This is the canonical method for defining a variable in Program Space.

To read back flash data, use the pgm_read_∗() macros defined in <avr/pgmspace.h>. All Program Memoryhandling macros are defined there.

There is also a way to create a method to define variables in Program Memory that is common between the two compilers(IAR and AVR GCC). Create a header file that has these definitions:

#if defined(__ICCAVR__) // IAR C Compiler#define FLASH_DECLARE(x) __flash x#endif#if defined(__GNUC__) // GNU Compiler#define FLASH_DECLARE(x) x __attribute__((__progmem__))#endif

This code snippet checks for the IAR compiler or for the GCC compiler and defines a macro FLASH_DECLARE(x)that will declare a variable in Program Memory using the appropriate method based on the compiler that is being used.Then you would used it like so:

FLASH_DECLARE(int mydata[] = ...);

10.6 Non-Returning main()

To declare main() to be a non-returning function in IAR, it is done like this:

__C_task void main(void){

// code}


10.7 Locking Registers 47

To do the equivalent in AVR GCC, do this:

void main(void) __attribute__((noreturn));

void main(void){

//...}

Note

See the GCC User Manual for more information on Function Attributes.

In AVR GCC, a prototype for main() is required so you can declare the function attribute to specify that the main()function is of type "noreturn". Then, define main() as normal. Note that the return type for main() is now void.

10.7 Locking Registers

The IAR compiler allows a user to lock general registers from r15 and down by using compiler options and this keywordsyntax:

__regvar __no_init volatile unsigned int filteredTimeSinceCommutation @14;

This line locks r14 for use only when explicitly referenced in your code thorugh the var name "filteredTimeSince←↩Commutation". This means that the compiler cannot dispose of it at its own will.

To do this in AVR GCC, do this:


Typically, it should be possible to use r2 through r15 that way.

Note

Do not reserve r0 or r1 as these are used internally by the compiler for a temporary register and for a zero value.Locking registers is not recommended in AVR GCC as it removes this register from the control of the compiler,which may make code generation worse. Use at your own risk.

11 Frequently Asked Questions

11.1 FAQ Index

1. My program doesn’t recognize a variable updated within an interrupt routine

2. I get "undefined reference to..." for functions like "sin()"

3. How to permanently bind a variable to a register?

4. How to modify MCUCR or WDTCR early?

5. What is all this _BV() stuff about?

6. Can I use C++ on the AVR?

7. Shouldn’t I initialize all my variables?


48 CONTENTS

8. Why do some 16-bit timer registers sometimes get trashed?

9. How do I use a #define’d constant in an asm statement?

10. Why does the PC randomly jump around when single-stepping through my program in avr-gdb?

11. How do I trace an assembler file in avr-gdb?

12. How do I pass an IO port as a parameter to a function?

13. What registers are used by the C compiler?

14. How do I put an array of strings completely in ROM?

15. How to use external RAM?

16. Which -O flag to use?

17. How do I relocate code to a fixed address?

18. My UART is generating nonsense! My ATmega128 keeps crashing! Port F is completely broken!

19. Why do all my "foo...bar" strings eat up the SRAM?

20. Why does the compiler compile an 8-bit operation that uses bitwise operators into a 16-bit operation in assembly?

21. How to detect RAM memory and variable overlap problems?

22. Is it really impossible to program the ATtinyXX in C?

23. What is this "clock skew detected" message?

24. Why are (many) interrupt flags cleared by writing a logical 1?

25. Why have "programmed" fuses the bit value 0?

26. Which AVR-specific assembler operators are available?

27. Why are interrupts re-enabled in the middle of writing the stack pointer?

28. Why are there five different linker scripts?

29. How to add a raw binary image to linker output?

30. How do I perform a software reset of the AVR?

31. I am using floating point math. Why is the compiled code so big? Why does my code not work?

32. What pitfalls exist when writing reentrant code?

33. Why are some addresses of the EEPROM corrupted (usually address zero)?

34. Why is my baud rate wrong?

35. On a device with more than 128 KiB of flash, how to make function pointers work?

36. Why is assigning ports in a "chain" a bad idea?


11.2 My program doesn’t recognize a variable updated within an interrupt routine 49

11.2 My program doesn’t recognize a variable updated within an interrupt routine

When using the optimizer, in a loop like the following one:

uint8_t flag;...ISR(SOME_vect) {

flag = 1;}...

while (flag == 0) {...

}

the compiler will typically access flag only once, and optimize further accesses completely away, since its code pathanalysis shows that nothing inside the loop could change the value of flag anyway. To tell the compiler that this variablecould be changed outside the scope of its code path analysis (e. g. from within an interrupt routine), the variable needsto be declared like:

volatile uint8_t flag;

Back to FAQ Index.

11.3 I get "undefined reference to..." for functions like "sin()"

In order to access the mathematical functions that are declared in <math.h>, the linker needs to be told to also linkthe mathematical library, libm.a.

Typically, system libraries like libm.a are given to the final C compiler command line that performs the linking step byadding a flag -lm at the end. (That is, the initial lib and the filename suffix from the library are written immediately aftera -l flag. So for a libfoo.a library, -lfoo needs to be provided.) This will make the linker search the library in a pathknown to the system.

An alternative would be to specify the full path to the libm.a file at the same place on the command line, i. e. after allthe object files (∗.o). However, since this requires knowledge of where the build system will exactly find those libraryfiles, this is deprecated for system libraries.

Back to FAQ Index.

11.4 How to permanently bind a variable to a register?

This can be done with


Typically, it should be safe to use r2 through r7 that way.

Registers r8 through r15 can be used for argument passing by the compiler in case many or long arguments are beingpassed to callees. If this is not the case throughout the entire application, these registers could be used for registervariables as well.

Extreme care should be taken that the entire application is compiled with a consistent set of register-allocated variables,including possibly used library functions.

See C Names Used in Assembler Code for more details.

Back to FAQ Index.


50 CONTENTS

11.5 How to modify MCUCR or WDTCR early?

The method of early initialization (MCUCR, WDTCR or anything else) is different (and more flexible) in the current version.Basically, write a small assembler file which looks like this:

;; begin xram.S

#include <avr/io.h>

.section .init1,"ax",@progbits

ldi r16,_BV(SRE) | _BV(SRW)out _SFR_IO_ADDR(MCUCR),r16

;; end xram.S

Assemble it, link the resulting xram.o with other files in your program, and this piece of code will be inserted ininitialization code, which is run right after reset. See the linker script for comments about the new .initN sections(which one to use, etc.).

The advantage of this method is that you can insert any initialization code you want (just remember that this is very earlystartup – no stack and no __zero_reg__ yet), and no program memory space is wasted if this feature is not used.

There should be no need to modify linker scripts anymore, except for some very special cases. It is best to leave __←↩stack at its default value (end of internal SRAM – faster, and required on some devices like ATmega161 because oferrata), and add -Wl,-Tdata,0x801100 to start the data section above the stack.

For more information on using sections, see Memory Sections. There is also an example for Using Sections in C Code.Note that in C code, any such function would preferably be placed into section .init3 as the code in .init2 ensures theinternal register __zero_reg__ is already cleared.

Back to FAQ Index.

11.6 What is all this _BV() stuff about?

When performing low-level output work, which is a very central point in microcontroller programming, it is quite commonthat a particular bit needs to be set or cleared in some IO register. While the device documentation provides mnemonicnames for the various bits in the IO registers, and the AVR device-specific IO definitions reflect these names in definitionsfor numerical constants, a way is needed to convert a bit number (usually within a byte register) into a byte value thatcan be assigned directly to the register. However, sometimes the direct bit numbers are needed as well (e. g. in anSBI() instruction), so the definitions cannot usefully be made as byte values in the first place.

So in order to access a particular bit number as a byte value, use the _BV() macro. Of course, the implementation ofthis macro is just the usual bit shift (which is done by the compiler anyway, thus doesn’t impose any run-time penalty),so the following applies:

_BV(3) => 1 << 3 => 0x08

However, using the macro often makes the program better readable.

"BV" stands for "bit value", in case someone might ask you. :-)

Example: clock timer 2 with full IO clock (CS2x = 0b001), toggle OC2 output on compare match (COM2x = 0b01), andclear timer on compare match (CTC2 = 1). Make OC2 (PD7) an output.

TCCR2 = _BV(COM20)|_BV(CTC2)|_BV(CS20);DDRD = _BV(PD7);

Back to FAQ Index.


11.7 Can I use C++ on the AVR? 51

11.7 Can I use C++ on the AVR?

Basically yes, C++ is supported (assuming your compiler has been configured and compiled to support it, of course).Source files ending in .cc, .cpp or .C will automatically cause the compiler frontend to invoke the C++ compiler. Alterna-tively, the C++ compiler could be explicitly called by the name avr-c++.

However, there’s currently no support for libstdc++, the standard support library needed for a complete C++ imple-mentation. This imposes a number of restrictions on the C++ programs that can be compiled. Among them are:

• Obviously, none of the C++ related standard functions, classes, and template classes are available.

• The operators new and delete are not implemented, attempting to use them will cause the linker to complainabout undefined external references. (This could perhaps be fixed.)

• Some of the supplied include files are not C++ safe, i. e. they need to be wrapped into

extern "C" { . . . }

(This could certainly be fixed, too.)

• Exceptions are not supported. Since exceptions are enabled by default in the C++ frontend, they explicitly needto be turned off using -fno-exceptions in the compiler options. Failing this, the linker will complain about anundefined external reference to __gxx_personality_sj0.

Constructors and destructors are supported though, including global ones.

When programming C++ in space- and runtime-sensitive environments like microcontrollers, extra care should be takento avoid unwanted side effects of the C++ calling conventions like implied copy constructors that could be called uponfunction invocation etc. These things could easily add up into a considerable amount of time and program memorywasted. Thus, casual inspection of the generated assembler code (using the -S compiler option) seems to be warranted.

Back to FAQ Index.

11.8 Shouldn’t I initialize all my variables?

Global and static variables are guaranteed to be initialized to 0 by the C standard. avr-gcc does this by placing theappropriate code into section .init4 (see The .initN Sections). With respect to the standard, this sentence is somewhatsimplified (because the standard allows for machines where the actual bit pattern used differs from all bits being 0), butfor the AVR target, in general, all integer-type variables are set to 0, all pointers to a NULL pointer, and all floating-pointvariables to 0.0.

As long as these variables are not initialized (i. e. they don’t have an equal sign and an initialization expression to theright within the definition of the variable), they go into the .bss section of the file. This section simply records the sizeof the variable, but otherwise doesn’t consume space, neither within the object file nor within flash memory. (Of course,being a variable, it will consume space in the target’s SRAM.)

In contrast, global and static variables that have an initializer go into the .data section of the file. This will cause them toconsume space in the object file (in order to record the initializing value), and in the flash ROM of the target device. Thelatter is needed since the flash ROM is the only way that the compiler can tell the target device the value this variable isgoing to be initialized to.

Now if some programmer "wants to make doubly sure" their variables really get a 0 at program startup, and adds aninitializer just containing 0 on the right-hand side, they waste space. While this waste of space applies to virtually anyplatform C is implemented on, it’s usually not noticeable on larger machines like PCs, while the waste of flash ROMstorage can be very painful on a small microcontroller like the AVR.

So in general, variables should only be explicitly initialized if the initial value is non-zero.


52 CONTENTS

Note

Recent versions of GCC are now smart enough to detect this situation, and revert variables that are explicitlyinitialized to 0 to the .bss section. Still, other compilers might not do that optimization, and as the C standardguarantees the initialization, it is safe to rely on it.

Back to FAQ Index.

11.9 Why do some 16-bit timer registers sometimes get trashed?

Some of the timer-related 16-bit IO registers use a temporary register (called TEMP in the Atmel datasheet) to guaranteean atomic access to the register despite the fact that two separate 8-bit IO transfers are required to actually move thedata. Typically, this includes access to the current timer/counter value register (TCNTn), the input capture register (I←↩CRn), and write access to the output compare registers (OCRnM). Refer to the actual datasheet for each device’s set ofregisters that involves the TEMP register.

When accessing one of the registers that use TEMP from the main application, and possibly any other one from withinan interrupt routine, care must be taken that no access from within an interrupt context could clobber the TEMP registerdata of an in-progress transaction that has just started elsewhere.

To protect interrupt routines against other interrupt routines, it’s usually best to use the ISR() macro when declaring theinterrupt function, and to ensure that interrupts are still disabled when accessing those 16-bit timer registers.

Within the main program, access to those registers could be encapsulated in calls to the cli() and sei() macros. Ifthe status of the global interrupt flag before accessing one of those registers is uncertain, something like the followingexample code can be used.

uint16_tread_timer1(void){

uint8_t sreg;uint16_t val;

sreg = SREG;cli();val = TCNT1;SREG = sreg;

return val;}

Back to FAQ Index.

11.10 How do I use a #define’d constant in an asm statement?

So you tried this:

asm volatile("sbi 0x18,0x07;");

Which works. When you do the same thing but replace the address of the port by its macro name, like this:

asm volatile("sbi PORTB,0x07;");

you get a compilation error: "Error: constant value required".

PORTB is a precompiler definition included in the processor specific file included in avr/io.h. As you may know, theprecompiler will not touch strings and PORTB, instead of 0x18, gets passed to the assembler. One way to avoid thisproblem is:

asm volatile("sbi %0, 0x07" : "I" (_SFR_IO_ADDR(PORTB)):);


11.11 Why does the PC randomly jump around when single-stepping through my program in avr-gdb? 53

Note

For C programs, rather use the standard C bit operators instead, so the above would be expressed as PORTB |=(1 << 7). The optimizer will take care to transform this into a single SBI instruction, assuming the operandsallow for this.

Back to FAQ Index.

11.11 Why does the PC randomly jump around when single-stepping through my program in avr-gdb?

When compiling a program with both optimization (-O) and debug information (-g) which is fortunately possible inavr-gcc, the code watched in the debugger is optimized code. While it is not guaranteed, very often this code runswith the exact same optimizations as it would run without the -g switch.

This can have unwanted side effects. Since the compiler is free to reorder code execution as long as the semanticsdo not change, code is often rearranged in order to make it possible to use a single branch instruction for conditionaloperations. Branch instructions can only cover a short range for the target PC (-63 through +64 words from the currentPC). If a branch instruction cannot be used directly, the compiler needs to work around it by combining a skip instructiontogether with a relative jump (rjmp) instruction, which will need one additional word of ROM.

Another side effect of optimization is that variable usage is restricted to the area of code where it is actually used. So ifa variable was placed in a register at the beginning of some function, this same register can be re-used later on if thecompiler notices that the first variable is no longer used inside that function, even though the variable is still in lexicalscope. When trying to examine the variable in avr-gdb, the displayed result will then look garbled.

So in order to avoid these side effects, optimization can be turned off while debugging. However, some of theseoptimizations might also have the side effect of uncovering bugs that would otherwise not be obvious, so it must be notedthat turning off optimization can easily change the bug pattern. In most cases, you are better off leaving optimizationsenabled while debugging.

Back to FAQ Index.

11.12 How do I trace an assembler file in avr-gdb?

When using the -g compiler option, avr-gcc only generates line number and other debug information for C (and C++)files that pass the compiler. Functions that don’t have line number information will be completely skipped by a singlestep command in gdb. This includes functions linked from a standard library, but by default also functions defined inan assembler source file, since the -g compiler switch does not apply to the assembler.

So in order to debug an assembler input file (possibly one that has to be passed through the C preprocessor), it’s theassembler that needs to be told to include line-number information into the output file. (Other debug information likedata types and variable allocation cannot be generated, since unlike a compiler, the assembler basically doesn’t knowabout this.) This is done using the (GNU) assembler option -gstabs.

Example:

$ avr-as -mmcu=atmega128 --gstabs -o foo.o foo.s

When the assembler is not called directly but through the C compiler frontend (either implicitly by passing a sourcefile ending in .S, or explicitly using -x assembler-with-cpp), the compiler frontend needs to be told to pass the-gstabs option down to the assembler. This is done using -Wa,-gstabs. Please take care to only pass this optionwhen compiling an assembler input file. Otherwise, the assembler code that results from the C compilation stage willalso get line number information, which confuses the debugger.


54 CONTENTS

Note

You can also use -Wa,-gstabs since the compiler will add the extra ’-’ for you.

Example:

$ EXTRA_OPTS="-Wall -mmcu=atmega128 -x assembler-with-cpp"$ avr-gcc -Wa,--gstabs ${EXTRA_OPTS} -c -o foo.o foo.S

Also note that the debugger might get confused when entering a piece of code that has a non-local label before, since itthen takes this label as the name of a new function that appears to have been entered. Thus, the best practice to avoidthis confusion is to only use non-local labels when declaring a new function, and restrict anything else to local labels.Local labels consist just of a number only. References to these labels consist of the number, followed by the letter b fora backward reference, or f for a forward reference. These local labels may be re-used within the source file, referenceswill pick the closest label with the same number and given direction.

Example:

myfunc: push r16push r17push r18push YLpush YH...eor r16, r16 ; start loopldi YL, lo8(sometable)ldi YH, hi8(sometable)rjmp 2f ; jump to loop test at end

1: ld r17, Y+ ; loop continues here...breq 1f ; return from myfunc prematurely...inc r16

2: cmp r16, r18brlo 1b ; jump back to top of loop

1: pop YHpop YLpop r18pop r17pop r16ret

Back to FAQ Index.

11.13 How do I pass an IO port as a parameter to a function?

Consider this example code:

#include <inttypes.h>#include <avr/io.h>

voidset_bits_func_wrong (volatile uint8_t port, uint8_t mask){

port |= mask;}

voidset_bits_func_correct (volatile uint8_t *port, uint8_t mask){

*port |= mask;}

#define set_bits_macro(port,mask) ((port) |= (mask))

int main (void){


11.13 How do I pass an IO port as a parameter to a function? 55

set_bits_func_wrong (PORTB, 0xaa);set_bits_func_correct (&PORTB, 0x55);set_bits_macro (PORTB, 0xf0);

return (0);}

The first function will generate object code which is not even close to what is intended. The major problem arises whenthe function is called. When the compiler sees this call, it will actually pass the value of the PORTB register (using anIN instruction), instead of passing the address of PORTB (e.g. memory mapped io addr of 0x38, io port 0x18 for themega128). This is seen clearly when looking at the disassembly of the call:

set_bits_func_wrong (PORTB, 0xaa);10a: 6a ea ldi r22, 0xAA ; 17010c: 88 b3 in r24, 0x18 ; 2410e: 0e 94 65 00 call 0xca

So, the function, once called, only sees the value of the port register and knows nothing about which port it came from.At this point, whatever object code is generated for the function by the compiler is irrelevant. The interested reader canexamine the full disassembly to see that the function’s body is completely fubar.

The second function shows how to pass (by reference) the memory mapped address of the io port to the function sothat you can read and write to it in the function. Here’s the object code generated for the function call:

set_bits_func_correct (&PORTB, 0x55);112: 65 e5 ldi r22, 0x55 ; 85114: 88 e3 ldi r24, 0x38 ; 56116: 90 e0 ldi r25, 0x00 ; 0118: 0e 94 7c 00 call 0xf8

You can clearly see that 0x0038 is correctly passed for the address of the io port. Looking at the disassembled objectcode for the body of the function, we can see that the function is indeed performing the operation we intended:

voidset_bits_func_correct (volatile uint8_t *port, uint8_t mask){

f8: fc 01 movw r30, r24

*port |= mask;fa: 80 81 ld r24, Zfc: 86 2b or r24, r22fe: 80 83 st Z, r24

}100: 08 95 ret

Notice that we are accessing the io port via the LD and ST instructions.

The port parameter must be volatile to avoid a compiler warning.

Note

Because of the nature of the IN and OUT assembly instructions, they can not be used inside the function whenpassing the port in this way. Readers interested in the details should consult the Instruction Set datasheet.

Finally we come to the macro version of the operation. In this contrived example, the macro is the most efficient methodwith respect to both execution speed and code size:

set_bits_macro (PORTB, 0xf0);11c: 88 b3 in r24, 0x18 ; 2411e: 80 6f ori r24, 0xF0 ; 240120: 88 bb out 0x18, r24 ; 24


56 CONTENTS

Of course, in a real application, you might be doing a lot more in your function which uses a passed by reference io portaddress and thus the use of a function over a macro could save you some code space, but still at a cost of executionspeed.

Care should be taken when such an indirect port access is going to one of the 16-bit IO registers where the orderof write access is critical (like some timer registers). All versions of avr-gcc up to 3.3 will generate instructions thatuse the wrong access order in this situation (since with normal memory operands where the order doesn’t matter, thissometimes yields shorter code).

See http://mail.nongnu.org/archive/html/avr-libc-dev/2003-01/msg00044.html for apossible workaround.

avr-gcc versions after 3.3 have been fixed in a way where this optimization will be disabled if the respective pointervariable is declared to be volatile, so the correct behaviour for 16-bit IO ports can be forced that way.

Back to FAQ Index.

11.14 What registers are used by the C compiler?

• Data types:char is 8 bits, int is 16 bits, long is 32 bits, long long is 64 bits, float and double are 32 bits (thisis the only supported floating point format), pointers are 16 bits (function pointers are word addresses, to allowaddressing up to 128K program memory space). There is a -mint8 option (see Options for the C compileravr-gcc) to make int 8 bits, but that is not supported by avr-libc and violates C standards (int must be at least16 bits). It may be removed in a future release.

• Call-used registers (r18-r27, r30-r31):May be allocated by gcc for local data. You may use them freely in assembler subroutines. Calling C subroutinescan clobber any of them - the caller is responsible for saving and restoring.

• Call-saved registers (r2-r17, r28-r29):May be allocated by gcc for local data. Calling C subroutines leaves them unchanged. Assembler subroutinesare responsible for saving and restoring these registers, if changed. r29:r28 (Y pointer) is used as a frame pointer(points to local data on stack) if necessary. The requirement for the callee to save/preserve the contents of theseregisters even applies in situations where the compiler assigns them for argument passing.

• Fixed registers (r0, r1):Never allocated by gcc for local data, but often used for fixed purposes:

r0 - temporary register, can be clobbered by any C code (except interrupt handlers which save it), may be used toremember something for a while within one piece of assembler code

r1 - assumed to be always zero in any C code, may be used to remember something for a while within one pieceof assembler code, but must then be cleared after use (clr r1). This includes any use of the [f]mul[s[u]]instructions, which return their result in r1:r0. Interrupt handlers save and clear r1 on entry, and restore r1 on exit (incase it was non-zero).

• Function call conventions:Arguments - allocated left to right, r25 to r8. All arguments are aligned to start in even-numbered registers (odd-sized arguments, including char, have one free register above them). This allows making better use of the movwinstruction on the enhanced core.

If too many, those that don’t fit are passed on the stack.

Return values: 8-bit in r24 (not r25!), 16-bit in r25:r24, up to 32 bits in r22-r25, up to 64 bits in r18-r25. 8-bit return valuesare zero/sign-extended to 16 bits by the called function (unsigned char is more efficient than signed char -just clr r25). Arguments to functions with variable argument lists (printf etc.) are all passed on stack, and char isextended to int.


http://mail.nongnu.org/archive/html/avr-libc-dev/2003-01/msg00044.html

11.15 How do I put an array of strings completely in ROM? 57

Warning

There was no such alignment before 2000-07-01, including the old patches for gcc-2.95.2. Check your old assem-bler subroutines, and adjust them accordingly.

Back to FAQ Index.

11.15 How do I put an array of strings completely in ROM?

There are times when you may need an array of strings which will never be modified. In this case, you don’t want towaste ram storing the constant strings. The most obvious (and incorrect) thing to do is this:

#include <avr/pgmspace.h>

PGM_P array[2] PROGMEM = {"Foo","Bar"

};

int main (void){

char buf[32];strcpy_P (buf, array[1]);return 0;

}

The result is not what you want though. What you end up with is the array stored in ROM, while the individual stringsend up in RAM (in the .data section).

To work around this, you need to do something like this:

#include <avr/pgmspace.h>

const char foo[] PROGMEM = "Foo";const char bar[] PROGMEM = "Bar";

PGM_P array[2] PROGMEM = {foo,bar

};

int main (void){

char buf[32];PGM_P p;int i;

memcpy_P(&p, &array[i], sizeof(PGM_P));strcpy_P(buf, p);return 0;

}

Looking at the disassembly of the resulting object file we see that array is in flash as such:

00000026 <array>:26: 2e 00 .word 0x002e ; ????28: 2a 00 .word 0x002a ; ????

0000002a <bar>:2a: 42 61 72 00 Bar.

0000002e <foo>:2e: 46 6f 6f 00 Foo.

foo is at addr 0x002e.bar is at addr 0x002a.


58 CONTENTS

array is at addr 0x0026.

Then in main we see this:

memcpy_P(&p, &array[i], sizeof(PGM_P));70: 66 0f add r22, r2272: 77 1f adc r23, r2374: 6a 5d subi r22, 0xDA ; 21876: 7f 4f sbci r23, 0xFF ; 25578: 42 e0 ldi r20, 0x02 ; 27a: 50 e0 ldi r21, 0x00 ; 07c: ce 01 movw r24, r287e: 81 96 adiw r24, 0x21 ; 3380: 08 d0 rcall .+16 ; 0x92

This code reads the pointer to the desired string from the ROM table array into a register pair.

The value of i (in r22:r23) is doubled to accommodate for the word offset required to access array[], then the addressof array (0x26) is added, by subtracting the negated address (0xffda). The address of variable p is computed by addingits offset within the stack frame (33) to the Y pointer register, and memcpy_P is called.

strcpy_P(buf, p);82: 69 a1 ldd r22, Y+33 ; 0x2184: 7a a1 ldd r23, Y+34 ; 0x2286: ce 01 movw r24, r2888: 01 96 adiw r24, 0x01 ; 18a: 0c d0 rcall .+24 ; 0xa4

This will finally copy the ROM string into the local buffer buf.

Variable p (located at Y+33) is read, and passed together with the address of buf (Y+1) to strcpy_P. This will copythe string from ROM to buf.

Note that when using a compile-time constant index, omitting the first step (reading the pointer from ROM via memcpy←↩_P) usually remains unnoticed, since the compiler would then optimize the code for accessing array at compile-time.

Back to FAQ Index.

11.16 How to use external RAM?

Well, there is no universal answer to this question; it depends on what the external RAM is going to be used for.

Basically, the bit SRE (SRAM enable) in the MCUCR register needs to be set in order to enable the external memoryinterface. Depending on the device to be used, and the application details, further registers affecting the externalmemory operation like XMCRA and XMCRB, and/or further bits in MCUCR might be configured. Refer to the datasheetfor details.

If the external RAM is going to be used to store the variables from the C program (i. e., the .data and/or .bss segment)in that memory area, it is essential to set up the external memory interface early during the device initialization so theinitialization of these variable will take place. Refer to How to modify MCUCR or WDTCR early? for a description howto do this using few lines of assembler code, or to the chapter about memory sections for an example written in C.

The explanation of malloc() contains a discussion about the use of internal RAM vs. external RAM in particular withrespect to the various possible locations of the heap (area reserved for malloc()). It also explains the linker command-line options that are required to move the memory regions away from their respective standard locations in internalRAM.

Finally, if the application simply wants to use the additional RAM for private data storage kept outside the domain of theC compiler (e. g. through a char ∗ variable initialized directly to a particular address), it would be sufficient to defer theinitialization of the external RAM interface to the beginning of main(), so no tweaking of the .init3 section is necessary.The same applies if only the heap is going to be located there, since the application start-up code does not affect theheap.


11.17 Which -O flag to use? 59

It is not recommended to locate the stack in external RAM. In general, accessing external RAM is slower than internalRAM, and errata of some AVR devices even prevent this configuration from working properly at all.

Back to FAQ Index.

11.17 Which -O flag to use?

There’s a common misconception that larger numbers behind the -O option might automatically cause "better" opti-mization. First, there’s no universal definition for "better", with optimization often being a speed vs. code size trade off.See the detailed discussion for which option affects which part of the code generation.

A test case was run on an ATmega128 to judge the effect of compiling the library itself using different optimization levels.The following table lists the results. The test case consisted of around 2 KB of strings to sort. Test #1 used qsort() usingthe standard library strcmp(), test #2 used a function that sorted the strings by their size (thus had two calls to strlen()per invocation).

When comparing the resulting code size, it should be noted that a floating point version of fvprintf() was linked into thebinary (in order to print out the time elapsed) which is entirely not affected by the different optimization levels, and addedabout 2.5 KB to the code.

Optimization flags Size of .text Time for test #1 Time for test #2-O3 6898 903 µs 19.7 ms-O2 6666 972 µs 20.1 ms-Os 6618 955 µs 20.1 ms-Os -mcall-prologues 6474 972 µs 20.1 ms

(The difference between 955 µs and 972 µs was just a single timer-tick, so take this with a grain of salt.)

So generally, it seems -Os -mcall-prologues is the most universal "best" optimization level. Only applicationsthat need to get the last few percent of speed benefit from using -O3.

Back to FAQ Index.

11.18 How do I relocate code to a fixed address?

First, the code should be put into a new named section. This is done with a section attribute:

__attribute__ ((section (".bootloader")))

In this example, .bootloader is the name of the new section. This attribute needs to be placed after the prototype of anyfunction to force the function into the new section.

void boot(void) __attribute__ ((section (".bootloader")));

To relocate the section to a fixed address the linker flag -section-start is used. This option can be passed to thelinker using the -Wl compiler option:

-Wl,--section-start=.bootloader=0x1E000

The name after section-start is the name of the section to be relocated. The number after the section name is thebeginning address of the named section.

Back to FAQ Index.


60 CONTENTS

11.19 My UART is generating nonsense! My ATmega128 keeps crashing! Port F is completely broken!

Well, certain odd problems arise out of the situation that the AVR devices as shipped by Atmel often come with a defaultfuse bit configuration that doesn’t match the user’s expectations. Here is a list of things to care for:

• All devices that have an internal RC oscillator ship with the fuse enabled that causes the device to run off thisoscillator, instead of an external crystal. This often remains unnoticed until the first attempt is made to usesomething critical in timing, like UART communication.

• The ATmega128 ships with the fuse enabled that turns this device into ATmega103 compatibility mode. Thismeans that some ports are not fully usable, and in particular that the internal SRAM is located at lower addresses.Since by default, the stack is located at the top of internal SRAM, a program compiled for an ATmega128 runningon such a device will immediately crash upon the first function call (or rather, upon the first function return).

• Devices with a JTAG interface have the JTAGEN fuse programmed by default. This will make the respective portpins that are used for the JTAG interface unavailable for regular IO.

Back to FAQ Index.

11.20 Why do all my "foo...bar" strings eat up the SRAM?

By default, all strings are handled as all other initialized variables: they occupy RAM (even though the compiler mightwarn you when it detects write attempts to these RAM locations), and occupy the same amount of flash ROM so theycan be initialized to the actual string by startup code. The compiler can optimize multiple identical strings into a singleone, but obviously only for one compilation unit (i. e., a single C source file).

That way, any string literal will be a valid argument to any C function that expects a const char ∗ argument.

Of course, this is going to waste a lot of SRAM. In Program Space String Utilities, a method is described how suchconstant data can be moved out to flash ROM. However, a constant string located in flash ROM is no longer a validargument to pass to a function that expects a const char ∗-type string, since the AVR processor needs the specialinstruction LPM to access these strings. Thus, separate functions are needed that take this into account. Many of thestandard C library functions have equivalents available where one of the string arguments can be located in flash ROM.Private functions in the applications need to handle this, too. For example, the following can be used to implementsimple debugging messages that will be sent through a UART:

#include <inttypes.h>#include <avr/io.h>#include <avr/pgmspace.h>

intuart_putchar(char c){

if (c == ’\n’)uart_putchar(’\r’);

loop_until_bit_is_set(USR, UDRE);UDR = c;return 0; /* so it could be used for fdevopen(), too */

}

voiddebug_P(const char *addr){

char c;

while ((c = pgm_read_byte(addr++)))uart_putchar(c);

}

intmain(void){

ioinit(); /* initialize UART, ... */


11.21 Why does the compiler compile an 8-bit operation that uses bitwise operators into a 16-bit operation inassembly? 61

debug_P(PSTR("foo was here\n"));return 0;

}

Note

By convention, the suffix _P to the function name is used as an indication that this function is going to accept a"program-space string". Note also the use of the PSTR() macro.

Back to FAQ Index.

11.21 Why does the compiler compile an 8-bit operation that uses bitwise operators into a 16-bit operation inassembly?

Bitwise operations in Standard C will automatically promote their operands to an int, which is (by default) 16 bits inavr-gcc.

To work around this use typecasts on the operands, including literals, to declare that the values are to be 8 bit operands.

This may be especially important when clearing a bit:

var &= ~mask; /* wrong way! */

The bitwise "not" operator (∼) will also promote the value in mask to an int. To keep it an 8-bit value, typecast beforethe "not" operator:

var &= (unsigned char)~mask;

Back to FAQ Index.

11.22 How to detect RAM memory and variable overlap problems?

You can simply run avr-nm on your output (ELF) file. Run it with the -n option, and it will sort the symbols numerically(by default, they are sorted alphabetically).

Look for the symbol _end, that’s the first address in RAM that is not allocated by a variable. (avr-gcc internally adds0x800000 to all data/bss variable addresses, so please ignore this offset.) Then, the run-time initialization code initializesthe stack pointer (by default) to point to the last available address in (internal) SRAM. Thus, the region between _endand the end of SRAM is what is available for stack. (If your application uses malloc(), which e. g. also can happen insideprintf(), the heap for dynamic memory is also located there. See Memory Areas and Using malloc().)

The amount of stack required for your application cannot be determined that easily. For example, if you recursively calla function and forget to break that recursion, the amount of stack required is infinite. :-) You can look at the generatedassembler code (avr-gcc ... -S), there’s a comment in each generated assembler file that tells you the framesize for each generated function. That’s the amount of stack required for this function, you have to add up that for allfunctions where you know that the calls could be nested.

Back to FAQ Index.

11.23 Is it really impossible to program the ATtinyXX in C?

While some small AVRs are not directly supported by the C compiler since they do not have a RAM-based stack (andsome do not even have RAM at all), it is possible anyway to use the general-purpose registers as a RAM replacementsince they are mapped into the data memory region.


62 CONTENTS

Bruce D. Lightner wrote an excellent description of how to do this, and offers this together with a toolkit on his web page:

http://lightner.net/avr/ATtinyAvrGcc.html

Back to FAQ Index.

11.24 What is this "clock skew detected" message?

It’s a known problem of the MS-DOS FAT file system. Since the FAT file system has only a granularity of 2 seconds formaintaining a file’s timestamp, and it seems that some MS-DOS derivative (Win9x) perhaps rounds up the current timeto the next second when calculating the timestamp of an updated file in case the current time cannot be represented inFAT’s terms, this causes a situation where make sees a "file coming from the future".

Since all make decisions are based on file timestamps, and their dependencies, make warns about this situation.

Solution: don’t use inferior file systems / operating systems. Neither Unix file systems nor HPFS (aka NTFS) doexperience that problem.

Workaround: after saving the file, wait a second before starting make. Or simply ignore the warning. If you are paranoid,execute a make clean all to make sure everything gets rebuilt.

In networked environments where the files are accessed from a file server, this message can also happen if the fileserver’s clock differs too much from the network client’s clock. In this case, the solution is to use a proper time keepingprotocol on both systems, like NTP. As a workaround, synchronize the client’s clock frequently with the server’s clock.

Back to FAQ Index.

11.25 Why are (many) interrupt flags cleared by writing a logical 1?

Usually, each interrupt has its own interrupt flag bit in some control register, indicating the specified interrupt conditionhas been met by representing a logical 1 in the respective bit position. When working with interrupt handlers, thisinterrupt flag bit usually gets cleared automatically in the course of processing the interrupt, sometimes by just callingthe handler at all, sometimes (e. g. for the U[S]ART) by reading a particular hardware register that will normally happenanyway when processing the interrupt.

From the hardware’s point of view, an interrupt is asserted as long as the respective bit is set, while global interruptsare enabled. Thus, it is essential to have the bit cleared before interrupts get re-enabled again (which usually happenswhen returning from an interrupt handler).

Only few subsystems require an explicit action to clear the interrupt request when using interrupt handlers. (The notableexception is the TWI interface, where clearing the interrupt indicates to proceed with the TWI bus hardware handshake,so it’s never done automatically.)

However, if no normal interrupt handlers are to be used, or in order to make extra sure any pending interrupt gets clearedbefore re-activating global interrupts (e. g. an external edge-triggered one), it can be necessary to explicitly clear therespective hardware interrupt bit by software. This is usually done by writing a logical 1 into this bit position. This seemsto be illogical at first, the bit position already carries a logical 1 when reading it, so why does writing a logical 1 to it clearthe interrupt bit?

The solution is simple: writing a logical 1 to it requires only a single OUT instruction, and it is clear that only this singleinterrupt request bit will be cleared. There is no need to perform a read-modify-write cycle (like, an SBI instruction),since all bits in these control registers are interrupt bits, and writing a logical 0 to the remaining bits (as it is done by thesimple OUT instruction) will not alter them, so there is no risk of any race condition that might accidentally clear anotherinterrupt request bit. So instead of writing

TIFR |= _BV(TOV0); /* wrong! */

simply use


http://lightner.net/avr/ATtinyAvrGcc.html

11.26 Why have "programmed" fuses the bit value 0? 63

TIFR = _BV(TOV0);

Back to FAQ Index.

11.26 Why have "programmed" fuses the bit value 0?

Basically, fuses are just a bit in a special EEPROM area. For technical reasons, erased E[E]PROM cells have all bits setto the value 1, so unprogrammed fuses also have a logical 1. Conversely, programmed fuse cells read out as bit value0.

Back to FAQ Index.

11.27 Which AVR-specific assembler operators are available?

See Pseudo-ops and operators.

Back to FAQ Index.

11.28 Why are interrupts re-enabled in the middle of writing the stack pointer?

When setting up space for local variables on the stack, the compiler generates code like this:

/* prologue: frame size=20 */push r28push r29in r28,__SP_L__in r29,__SP_H__sbiw r28,20in __tmp_reg__,__SREG__cliout __SP_H__,r29out __SREG__,__tmp_reg__out __SP_L__,r28

/* prologue end (size=10) */

It reads the current stack pointer value, decrements it by the required amount of bytes, then disables interrupts, writesback the high part of the stack pointer, writes back the saved SREG (which will eventually re-enable interrupts if theyhave been enabled before), and finally writes the low part of the stack pointer.

At the first glance, there’s a race between restoring SREG, and writing SPL. However, after enabling interrupts (eitherexplicitly by setting the I flag, or by restoring it as part of the entire SREG), the AVR hardware executes (at least) thenext instruction still with interrupts disabled, so the write to SPL is guaranteed to be executed with interrupts disabledstill. Thus, the emitted sequence ensures interrupts will be disabled only for the minimum time required to guaranteethe integrity of this operation.

Back to FAQ Index.

11.29 Why are there five different linker scripts?

From a comment in the source code:

Which one of the five linker script files is actually used depends on command line options given to ld.

A .x script file is the default script A .xr script is for linking without relocation (-r flag) A .xu script is like .xr but do createconstructors (-Ur flag) A .xn script is for linking with -n flag (mix text and data on same page). A .xbn script is for linkingwith -N flag (mix text and data on same page).

Back to FAQ Index.


64 CONTENTS

11.30 How to add a raw binary image to linker output?

The GNU linker avr-ld cannot handle binary data directly. However, there’s a companion tool called avr-objcopy.This is already known from the output side: it’s used to extract the contents of the linked ELF file into an Intel Hex loadfile.

avr-objcopy can create a relocatable object file from arbitrary binary input, like

avr-objcopy -I binary -O elf32-avr foo.bin foo.o

This will create a file named foo.o, with the contents of foo.bin. The contents will default to section .data, and twosymbols will be created named _binary_foo_bin_start and _binary_foo_bin_end. These symbols canbe referred to inside a C source to access these data.

If the goal is to have those data go to flash ROM (similar to having used the PROGMEM attribute in C source code), thesections have to be renamed while copying, and it’s also useful to set the section flags:

avr-objcopy --rename-section .data=.progmem.data,contents,alloc,load,readonly,data -I binary -O elf32-avrfoo.bin foo.o

Note that all this could be conveniently wired into a Makefile, so whenever foo.bin changes, it will trigger the recre-ation of foo.o, and a subsequent relink of the final ELF file.

Below are two Makefile fragments that provide rules to convert a .txt file to an object file, and to convert a .bin file to anobject file:

$(OBJDIR)/%.o : %.txt@echo Converting $<@cp $(<) $(*).tmp@echo -n 0 | tr 0 ’\000’ >> $(*).tmp@$(OBJCOPY) -I binary -O elf32-avr \--rename-section .data=.progmem.data,contents,alloc,load,readonly,data \--redefine-sym _binary_$*_tmp_start=$* \--redefine-sym _binary_$*_tmp_end=$*_end \--redefine-sym _binary_$*_tmp_size=$*_size_sym \$(*).tmp $(@)@echo "extern const char" $(*)"[] PROGMEM;" > $(*).h@echo "extern const char" $(*)_end"[] PROGMEM;" >> $(*).h@echo "extern const char" $(*)_size_sym"[];" >> $(*).h@echo "#define $(*)_size ((int)$(*)_size_sym)" >> $(*).h@rm $(*).tmp

$(OBJDIR)/%.o : %.bin@echo Converting $<@$(OBJCOPY) -I binary -O elf32-avr \--rename-section .data=.progmem.data,contents,alloc,load,readonly,data \--redefine-sym _binary_$*_bin_start=$* \--redefine-sym _binary_$*_bin_end=$*_end \--redefine-sym _binary_$*_bin_size=$*_size_sym \$(<) $(@)@echo "extern const char" $(*)"[] PROGMEM;" > $(*).h@echo "extern const char" $(*)_end"[] PROGMEM;" >> $(*).h@echo "extern const char" $(*)_size_sym"[];" >> $(*).h@echo "#define $(*)_size ((int)$(*)_size_sym)" >> $(*).h

Back to FAQ Index.

11.31 How do I perform a software reset of the AVR?

The canonical way to perform a software reset of non-XMega AVR’s is to use the watchdog timer. Enable the watchdogtimer to the shortest timeout setting, then go into an infinite, do-nothing loop. The watchdog will then reset the processor.

XMega parts have a specific bit RST_SWRST_bm in the RST.CTRL register, that generates a hardware reset. RST←↩_SWRST_bm is protected by the XMega Configuration Change Protection system.


11.32 I am using floating point math. Why is the compiled code so big? Why does my code not work? 65

The reason why using the watchdog timer or RST_SWRST_bm is preferable over jumping to the reset vector, is thatwhen the watchdog or RST_SWRST_bm resets the AVR, the registers will be reset to their known, default settings.Whereas jumping to the reset vector will leave the registers in their previous state, which is generally not a good idea.

CAUTION! Older AVRs will have the watchdog timer disabled on a reset. For these older AVRs, doing a soft resetby enabling the watchdog is easy, as the watchdog will then be disabled after the reset. On newer AVRs, once thewatchdog is enabled, then it stays enabled, even after a reset! For these newer AVRs a function needs to be addedto the .init3 section (i.e. during the startup code, before main()) to disable the watchdog early enough so it does notcontinually reset the AVR.

Here is some example code that creates a macro that can be called to perform a soft reset:

#include <avr/wdt.h>

...

#define soft_reset() \do \{ \

wdt_enable(WDTO_15MS); \for(;;) \{ \} \

} while(0)

For newer AVRs (such as the ATmega1281) also add this function to your code to then disable the watchdog after areset (e.g., after a soft reset):


...

// Function Pototypevoid wdt_init(void) __attribute__((naked)) __attribute__((section(".init3")));

...

// Function Implementationvoid wdt_init(void){

MCUSR = 0;wdt_disable();

return;}

Back to FAQ Index.

11.32 I am using floating point math. Why is the compiled code so big? Why does my code not work?

You are not linking in the math library from AVR-LibC. GCC has a library that is used for floating point operations, butit is not optimized for the AVR, and so it generates big code, or it could be incorrect. This can happen even when youare not using any floating point math functions from the Standard C library, but you are just doing floating point mathoperations.

When you link in the math library from AVR-LibC, those routines get replaced by hand-optimized AVR assembly and itproduces much smaller code.

See I get "undefined reference to..." for functions like "sin()" for more details on how to link in the math library.

Back to FAQ Index.


66 CONTENTS

11.33 What pitfalls exist when writing reentrant code?

Reentrant code means the ability for a piece of code to be called simultaneously from two or more threads. Attentionto re-enterability is needed when using a multi-tasking operating system, or when using interrupts since an interrupt isreally a temporary thread.

The code generated natively by gcc is reentrant. But, only some of the libraries in avr-libc are explicitly reentrant, andsome are known not to be reentrant. In general, any library call that reads and writes global variables (including I/Oregisters) is not reentrant. This is because more than one thread could read or write the same storage at the same time,unaware that other threads are doing the same, and create inconsistent and/or erroneous results.

A library call that is known not to be reentrant will work if it is used only within one thread and no other thread makesuse of a library call that shares common storage with it.

Below is a table of library calls with known issues.


11.33 What pitfalls exist when writing reentrant code? 67

Library call Reentrant Issue Workaround/Alternativerand(), random() Uses global variables to keep state

information.Use special reentrant versions:rand_r(), random_r().

strtod(), strtol(), strtoul() Uses the global variable errno toreturn success/failure.

Ignore errno, or protect calls withcli()/sei() or ATOMIC_BLOCK() ifthe application can tolerate it. Oruse sccanf() or sccanf_P() ifpossible.

malloc(), realloc(), calloc(), free() Uses the stack pointer and globalvariables to allocate and freememory.

Protect calls with cli()/sei() orATOMIC_BLOCK() if the applicationcan tolerate it. If using an OS, usethe OS provided memory allocatorsince the OS is likely modifying thestack pointer anyway.

fdevopen(), fclose() Uses calloc() and free(). Protect calls with cli()/sei() orATOMIC_BLOCK() if the applicationcan tolerate it. Or usefdev_setup_stream() orFDEV_SETUP_STREAM().Note: fclose() will only call free() ifthe stream has been opened withfdevopen().

eeprom_∗(), boot_∗() Accesses I/O registers. Protect calls with cli()/sei(),ATOMIC_BLOCK(), or use OSlocking.

pgm_∗_far() Accesses I/O register RAMPZ. Starting with GCC 4.3, RAMPZ isautomatically saved for ISRs, sonothing further is needed if onlyusing interrupts.Some OSes may automaticallypreserve RAMPZ during contextswitching. Check the OSdocumentation before assuming itdoes.Otherwise, protect calls withcli()/sei(), ATOMIC_BLOCK(), oruse explicit OS locking.

printf(), printf_P(), vprintf(),vprintf_P(), puts(), puts_P()

Alters flags and character count inglobal FILE stdout.

Use only in one thread. Or ifreturned character count isunimportant, do not use the ∗_Pversions.Note: Formatting to a string output,e.g. sprintf(), sprintf_P(), snprintf(),snprintf_P(), vsprintf(), vsprintf_P(),vsnprintf(), vsnprintf_P(), is threadsafe. The formatted string couldthen be followed by an fwrite() whichsimply calls the lower layer to sendthe string.


68 CONTENTS

fprintf(), fprintf_P(), vfprintf(),vfprintf_P(), fputs(), fputs_P()

Alters flags and character count inthe FILE argument. Problems canoccur if a global FILE is used frommultiple threads.

Assign each thread its own FILE foroutput. Or if returned charactercount is unimportant, do not use the∗_P versions.

assert() Contains an embedded fprintf().See above for fprintf().

See above for fprintf().

clearerr() Alters flags in the FILE argument. Assign each thread its own FILE foroutput.

getchar(), gets() Alters flags, character count, andunget buffer in global FILE stdin.

Use only in one thread. ∗∗∗

fgetc(), ungetc(), fgets(), scanf(),scanf_P(), fscanf(), fscanf_P(),vscanf(), vfscanf(), vfscanf_P(),fread()

Alters flags, character count, andunget buffer in the FILE argument.

Assign each thread its own FILE forinput. ∗∗∗Note: Scanning from a string, e.g.sscanf() and sscanf_P(), are threadsafe.

Note

It’s not clear one would ever want to do character input simultaneously from more than one thread anyway, butthese entries are included for completeness.

An effort will be made to keep this table up to date if any new issues are discovered or introduced.

Back to FAQ Index.

11.34 Why are some addresses of the EEPROM corrupted (usually address zero)?

The two most common reason for EEPROM corruption is either writing to the EEPROM beyond the datasheet endurancespecification, or resetting the AVR while an EEPROM write is in progress.

EEPROM writes can take up to tens of milliseconds to complete. So that the CPU is not tied up for that long of time,an internal state-machine handles EEPROM write requests. The EEPROM state-machine expects to have all of theEEPROM registers setup, then an EEPROM write request to start the process. Once the EEPROM state-machine hasstarted, changing EEPROM related registers during an EEPROM write is guaranteed to corrupt the EEPROM writeprocess. The datasheet always shows the proper way to tell when a write is in progress, so that the registers are notchanged by the user’s program. The EEPROM state-machine will always complete the write in progress unless poweris removed from the device.

As with all EEPROM technology, if power fails during an EEPROM write the state of the byte being written is undefined.

In older generation AVRs the EEPROM Address Register (EEAR) is initialized to zero on reset, be it from Brown OutDetect, Watchdog or the Reset Pin. If an EEPROM write has just started at the time of the reset, the write will becompleted, but now at address zero instead of the requested address. If the reset occurs later in the write process boththe requested address and address zero may be corrupted.

To distinguish which AVRs may exhibit the corrupt of address zero while a write is in process during a reset, look atthe "initial value" section for the EEPROM Address Register. If EEAR shows the initial value as 0x00 or 0x0000, thenaddress zero and possibly the one being written will be corrupted. Newer parts show the initial value as "undefined",these will not corrupt address zero during a reset (unless it was address zero that was being written).

EEPROMs have limited write endurance. The datasheet specifies the number of EEPROM writes that are guaranteedto function across the full temperature specification of the AVR, for a given byte. A read should always be performedbefore a write, to see if the value in the EEPROM actually needs to be written, so not to cause unnecessary EEPROMwear.

The failure mechanism for an overwritten byte is generally one of "stuck" bits, i. e. a bit will stay at a one or zero state


11.35 Why is my baud rate wrong? 69

regardless of the byte written. Also a write followed by a read may return the correct data, but the data will change withthe passage of time, due the EEPROM’s inability to hold a charge from the excessive write wear.

Back to FAQ Index.

11.35 Why is my baud rate wrong?

Some AVR datasheets give the following formula for calculating baud rates:

(F_CPU/(UART_BAUD_RATE*16L)-1)

Unfortunately that formula does not work with all combinations of clock speeds and baud rates due to integer truncationduring the division operator.

When doing integer division it is usually better to round to the nearest integer, rather than to the lowest. To do this add0.5 (i. e. half the value of the denominator) to the numerator before the division, resulting in the formula:

((F_CPU + UART_BAUD_RATE * 8L) / (UART_BAUD_RATE * 16L) - 1)

This is also the way it is implemented in <util/setbaud.h>: Helper macros for baud rate calculations.

Back to FAQ Index.

11.36 On a device with more than 128 KiB of flash, how to make function pointers work?

Function pointers beyond the "magical" 128 KiB barrier(s) on larger devices are supposed to be resolved through so-called trampolines by the linker, so the actual pointers used in the code can remain 16 bits wide.

In order for this to work, the option -mrelax must be given on the compiler command-line that is used to link the finalELF file. (Older compilers did not implement this option for the AVR, use -Wl,-relax instead.)

Back to FAQ Index.

11.37 Why is assigning ports in a "chain" a bad idea?

Suppose a number of IO port registers should get the value 0xff assigned. Conveniently, it is implemented like this:

DDRB = DDRD = 0xff;

According to the rules of the C language, this causes 0xff to be assigned to DDRD, then DDRD is read back, and thevalue is assigned to DDRB. The compiler stands no chance to optimize the readback away, as an IO port register isdeclared "volatile". Thus, chaining that kind of IO port assignments would better be avoided, using explicit assignmentsinstead:

DDRB = 0xff;DDRD = 0xff;

Even worse ist this, e. g. on an ATmega1281:

DDRA = DDRB = DDRC = DDRD = DDRE = DDRF = DDRG = 0xff;

The same happens as outlined above. However, when reading back register DDRG, this register only implements 6 outof the 8 bits, so the two topmost (unimplemented) bits read back as 0! Consequently, all remaining DDRx registers getassigned the value 0x3f, which does not match the intention of the developer in any way.

Back to FAQ Index.


70 CONTENTS

12 Building and Installing the GNU Tool Chain

This chapter shows how to build and install, from source code, a complete development environment for the AVRprocessors using the GNU toolset. There are two main sections, one for Linux, FreeBSD, and other Unix-like operatingsystems, and another section for Windows.

12.1 Building and Installing under Linux, FreeBSD, and Others

The default behaviour for most of these tools is to install every thing under the /usr/local directory. In order to keepthe AVR tools separate from the base system, it is usually better to install everything into /usr/local/avr. If the/usr/local/avr directory does not exist, you should create it before trying to install anything. You will need rootaccess to install there. If you don’t have root access to the system, you can alternatively install in your home directory,for example, in $HOME/local/avr. Where you install is a completely arbitrary decision, but should be consistent forall the tools.

You specify the installation directory by using the -prefix=dir option with the configure script. It is importantto install all the AVR tools in the same directory or some of the tools will not work correctly. To ensure consistency andsimplify the discussion, we will use $PREFIX to refer to whatever directory you wish to install in. You can set this as anenvironment variable if you wish as such (using a Bourne-like shell):

$ PREFIX=$HOME/local/avr$ export PREFIX

Note

Be sure that you have your PATH environment variable set to search the directory you install everything in beforeyou start installing anything. For example, if you use -prefix=$PREFIX, you must have $PREFIX/bin inyour exported PATH. As such:

$ PATH=$PATH:$PREFIX/bin$ export PATH

Warning

If you have CC set to anything other than avr-gcc in your environment, this will cause the configure script to fail.It is best to not have CC set at all.

Note

It is usually the best to use the latest released version of each of the tools.

12.2 Required Tools

• GNU Binutilshttp://sources.redhat.com/binutils/Installation

• GCChttp://gcc.gnu.org/Installation

• AVR LibChttp://savannah.gnu.org/projects/avr-libc/Installation


http://sources.redhat.com/binutils/

http://gcc.gnu.org/

http://savannah.gnu.org/projects/avr-libc/

12.3 Optional Tools 71

12.3 Optional Tools

You can develop programs for AVR devices without the following tools. They may or may not be of use for you.

• AVRDUDEhttp://savannah.nongnu.org/projects/avrdude/InstallationUsage Notes

• GDBhttp://sources.redhat.com/gdb/Installation

• SimulAVRhttp://savannah.gnu.org/projects/simulavr/Installation

• AVaRICEhttp://avarice.sourceforge.net/Installation

12.4 GNU Binutils for the AVR target

The binutils package provides all the low-level utilities needed in building and manipulating object files. Onceinstalled, your environment will have an AVR assembler (avr-as), linker (avr-ld), and librarian (avr-ar andavr-ranlib). In addition, you get tools which extract data from object files (avr-objcopy), dissassemble objectfile information (avr-objdump), and strip information from object files (avr-strip). Before we can build the Ccompiler, these tools need to be in place.

Download and unpack the source files:

$ bunzip2 -c binutils-<version>.tar.bz2 | tar xf -$ cd binutils-<version>

Note

Replace <version> with the version of the package you downloaded.If you obtained a gzip compressed file (.gz), use gunzip instead of bunzip2.

It is usually a good idea to configure and build binutils in a subdirectory so as not to pollute the source with thecompiled files. This is recommended by the binutils developers.

$ mkdir obj-avr$ cd obj-avr

The next step is to configure and build the tools. This is done by supplying arguments to the configure script thatenable the AVR-specific options.

$ ../configure --prefix=$PREFIX --target=avr --disable-nls


http://savannah.nongnu.org/projects/avrdude/

http://sources.redhat.com/gdb/

http://savannah.gnu.org/projects/simulavr/

http://avarice.sourceforge.net/

72 CONTENTS

If you don’t specify the -prefix option, the tools will get installed in the /usr/local hierarchy (i.e. the binaries willget installed in /usr/local/bin, the info pages get installed in /usr/local/info, etc.) Since these tools arechanging frequently, It is preferrable to put them in a location that is easily removed.

When configure is run, it generates a lot of messages while it determines what is available on your operating system.When it finishes, it will have created several Makefiles that are custom tailored to your platform. At this point, youcan build the project.

$ make

Note

BSD users should note that the project’s Makefile uses GNU make syntax. This means FreeBSD users mayneed to build the tools by using gmake.

If the tools compiled cleanly, you’re ready to install them. If you specified a destination that isn’t owned by your account,you’ll need root access to install them. To install:

$ make install

You should now have the programs from binutils installed into $PREFIX/bin. Don’t forget to set your PATH environ-ment variable before going to build avr-gcc.

12.5 GCC for the AVR target

Warning

You must install avr-binutils and make sure your path is set properly before installing avr-gcc.

The steps to build avr-gcc are essentially same as for binutils:

$ bunzip2 -c gcc-<version>.tar.bz2 | tar xf -$ cd gcc-<version>$ mkdir obj-avr$ cd obj-avr$ ../configure --prefix=$PREFIX --target=avr --enable-languages=c,c++ \

--disable-nls --disable-libssp --with-dwarf2$ make$ make install

To save your self some download time, you can alternatively download only the gcc-core-<version>.tar.bz2and gcc-c++-<version>.tar.bz2 parts of the gcc. Also, if you don’t need C++ support, you only need the corepart and should only enable the C language support. (Starting with GCC 4.7 releases, these split files are no longeravailable though.)

Note

Early versions of these tools did not support C++.The stdc++ libs are not included with C++ for AVR due to the size limitations of the devices.

12.6 AVR LibC


12.7 AVRDUDE 73

Warning

You must install avr-binutils, avr-gcc and make sure your path is set properly before installing avr-libc.

Note

If you have obtained the latest avr-libc from cvs, you will have to run the bootstrap script before using either ofthe build methods described below.

To build and install avr-libc:

$ gunzip -c avr-libc-<version>.tar.gz | tar xf -$ cd avr-libc-<version>$ ./configure --prefix=$PREFIX --build=‘./config.guess‘ --host=avr$ make$ make install

Optionally, generation of debug information can be requested with:

$ gunzip -c avr-libc-<version>.tar.gz | tar xf -$ cd avr-libc-<version>$ ./configure --prefix=$PREFIX --build=‘./config.guess‘ --host=avr \

--with-debug-info=DEBUG_INFO$ make$ make install

where DEBUG_INFO can be one of stabs, dwarf-2, or dwarf-4.

The default is to not generate any debug information, which is suitable for binary distributions of avr-libc, where the userdoes not have the source code installed the debug information would refer to.

12.7 AVRDUDE

Note

It has been ported to windows (via MinGW or cygwin), Linux and Solaris. Other Unix systems should be trivial toport to.

avrdude is part of the FreeBSD ports system. To install it, simply do the following:

# cd /usr/ports/devel/avrdude# make install

Note

Installation into the default location usually requires root permissions. However, running the program only requiresaccess permissions to the appropriate ppi(4) device.

Building and installing on other systems should use the configure system, as such:

$ gunzip -c avrdude-<version>.tar.gz | tar xf -$ cd avrdude-<version>$ mkdir obj-avr$ cd obj-avr$ ../configure --prefix=$PREFIX$ make$ make install


74 CONTENTS

12.8 GDB for the AVR target

GDB also uses the configure system, so to build and install:

$ bunzip2 -c gdb-<version>.tar.bz2 | tar xf -$ cd gdb-<version>$ mkdir obj-avr$ cd obj-avr$ ../configure --prefix=$PREFIX --target=avr$ make$ make install

Note

If you are planning on using avr-gdb, you will probably want to install either simulavr or avarice since avr-gdbneeds one of these to run as a a remote target backend.

12.9 SimulAVR

SimulAVR also uses the configure system, so to build and install:

$ gunzip -c simulavr-<version>.tar.gz | tar xf -$ cd simulavr-<version>$ mkdir obj-avr$ cd obj-avr$ ../configure --prefix=$PREFIX$ make$ make install

Note

You might want to have already installed avr-binutils, avr-gcc and avr-libc if you want to have the test programsbuilt in the simulavr source.

12.10 AVaRICE

Note

These install notes are not applicable to avarice-1.5 or older. You probably don’t want to use anything that oldanyways since there have been many improvements and bug fixes since the 1.5 release.

AVaRICE also uses the configure system, so to build and install:

$ gunzip -c avarice-<version>.tar.gz | tar xf -$ cd avarice-<version>$ mkdir obj-avr$ cd obj-avr$ ../configure --prefix=$PREFIX$ make$ make install

Note

AVaRICE uses the BFD library for accessing various binary file formats. You may need to tell the configure scriptwhere to find the lib and headers for the link to work. This is usually done by invoking the configure script like this(Replace <hdr_path> with the path to the bfd.h file on your system. Replace <lib_path> with the pathto libbfd.a on your system.):

$ CPPFLAGS=-I<hdr_path> LDFLAGS=-L<lib_path> ../configure --prefix=$PREFIX


12.11 Building and Installing under Windows 75

12.11 Building and Installing under Windows

Building and installing the toolchain under Windows requires more effort because all of the tools required for building,and the programs themselves, are mainly designed for running under a POSIX environment such as Unix and Linux.Windows does not natively provide such an environment.

There are two projects available that provide such an environment, Cygwin and MinGW. There are advantages anddisadvantages to both. Cygwin provides a very complete POSIX environment that allows one to build many Linux basedtools from source with very little or no source modifications. However, POSIX functionality is provided in the form ofa DLL that is linked to the application. This DLL has to be redistributed with your application and there are issues ifthe Cygwin DLL already exists on the installation system and different versions of the DLL. On the other hand, MinGWcan compile code as native Win32 applications. However, this means that programs designed for Unix and Linux (i.e.that use POSIX functionality) will not compile as MinGW does not provide that POSIX layer for you. Therefore mostprograms that compile on both types of host systems, usually must provide some sort of abstraction layer to allow anapplication to be built cross-platform.

MinGW does provide somewhat of a POSIX environment, called MSYS, that allows you to build Unix and Linux applica-tions as they woud normally do, with a configure step and a make step. Cygwin also provides such an environment.This means that building the AVR toolchain is very similar to how it is built in Linux, described above. The main differ-ences are in what the PATH environment variable gets set to, pathname differences, and the tools that are required tobuild the projects under Windows. We’ll take a look at the tools next.

12.12 Tools Required for Building the Toolchain for Windows

These are the tools that are currently used to build an AVR tool chain. This list may change, either the version of thetools, or the tools themselves, as improvements are made.

• MinGWDownload the MinGW Automated Installer, 20100909 (or later) http://sourceforge.net/projects/mingw/files/←↩Automated%20MinGW%20Installer/mingw-get-inst/mingw-get-inst-20100909/mingw-get-inst-20100909.←↩exe/download

– Run mingw-get-inst-20100909.exe

– In the installation wizard, keep the default values and press the "Next" button for all installer pages exceptfor the pages explicitly listed below.

In the installer page "Repository Catalogues", select the "Download latest repository catalogues" radio button, and pressthe "Next" button

• In the installer page "License Agreement", select the "I accept the agreement" radio button, and press the "Next"button

• In the installer page "Select Components", be sure to select these items:

– C compiler (default checked)

– C++ compiler

– Ada compiler

– MinGW Developer Toolkit (which includes "MSYS Basic System").

• Install.

Install Cygwin


http://sourceforge.net/projects/mingw/files/Automated%20MinGW%20Installer/mingw-get-inst/mingw-get-inst-20100909/mingw-get-inst-20100909.exe/download



76 CONTENTS

• Install everything, all users, UNIX line endings. This will take a long time. A fat internet pipe is highly recom-mended. It is also recommended that you download all to a directory first, and then install from that directory toyour machine.

Note

GMP, MPFR, and MPC are required to build GCC.GMP is a prequisite for building MPFR. Build GMP first.MPFR is a prerequisite for building MPC. Build MPFR second.

• Build GMP for MinGW

– Latest Version

– http://gmplib.org/

– Build script:

./configure 2>&1 | tee gmp-configure.logmake 2>&1 | tee gmp-make.logmake check 2>&1 | tee gmp-make-check.logmake install 2>&1 | tee gmp-make-install.log

– GMP headers will be installed under /usr/local/include and library installed under /usr/local/lib.

• Build MPFR for MinGW

– Latest Version

– http://www.mpfr.org/

– Build script:

./configure --with-gmp=/usr/local --disable-shared 2>&1 | tee mpfr-configure.logmake 2>&1 | tee mpfr-make.logmake check 2>&1 | tee mpfr-make-check.logmake install 2>&1 | tee mpfr-make-install.log

– MPFR headers will be installed under /usr/local/include and library installed under /usr/local/lib.

• Build MPC for MinGW

– Latest Version

– http://www.multiprecision.org/

– Build script:

./configure --with-gmp=/usr/local --with-mpfr=/usr/local --disable-shared 2>&1 | tee mpfr-configure.logmake 2>&1 | tee mpfr-make.logmake check 2>&1 | tee mpfr-make-check.logmake install 2>&1 | tee mpfr-make-install.log

– MPFR headers will be installed under /usr/local/include and library installed under /usr/local/lib.


http://gmplib.org/

http://www.mpfr.org/

http://www.multiprecision.org/

12.13 Building the Toolchain for Windows 77

Note

Doxygen is required to build AVR-LibC documentation.

• Install Doxygen

– Version 1.7.2– http://www.stack.nl/∼dimitri/doxygen/– Download and install.

NetPBM is required to build graphics in the AVR-LibC documentation.

• Install NetPBM

– Version 10.27.0– From the GNUWin32 project: http://gnuwin32.sourceforge.net/packages.html– Download and install.

fig2dev is required to build graphics in the AVR-LibC documentation.

• Install fig2dev

– Version 3.2 patchlevel 5c– From WinFig 4.62: http://www.schmidt-web-berlin.de/winfig/– Download the zip file version of WinFig– Unzip the download file and install fig2dev.exe in a location of your choice, somewhere in the PATH.– You may have to unzip and install related DLL files for fig2dev. In the version above, you have to install

QtCore4.dll and QtGui4.dll.

MikTeX is required to build various documentation.

• Install MiKTeX

– Version 2.9– http://miktex.org/

– Download and install.

Ghostscript is required to build various documentation.

• Install Ghostscript

– Version 9.00– http://www.ghostscript.com

– Download and install.– In the \bin subdirectory of the installaion, copy gswin32c.exe to gs.exe.

• Set the TEMP and TMP environment variables to c:\temp or to the short filename version. This helps toavoid NTVDM errors during building.

12.13 Building the Toolchain for Windows

All directories in the PATH enviornment variable should be specified using their short filename (8.3) version. This willalso help to avoid NTVDM errors during building. These short filenames can be specific to each machine.

Build the tools below in MinGW/MSYS.

• Binutils


http://www.stack.nl/~dimitri/doxygen/

http://gnuwin32.sourceforge.net/packages.html

http://www.schmidt-web-berlin.de/winfig/

http://miktex.org/

http://www.ghostscript.com

78 CONTENTS

– Open source code pacakge and patch as necessary.

– Configure and build in a directory outside of the source code tree.

– Set PATH, in order:

* <MikTex executables>

· <ghostscript executables>

* /usr/local/bin

* /usr/bin

* /bin

* /mingw/bin

* c:/cygwin/bin

* <install directory>/bin– Configure

CFLAGS=-D__USE_MINGW_ACCESS \../$archivedir/configure \

--prefix=$installdir \--target=avr \--disable-nls \--enable-doc \--datadir=$installdir/doc/binutils \--with-gmp=/usr/local \--with-mpfr=/usr/local \2>&1 | tee binutils-configure.log

– Make

make all html install install-html 2>&1 | tee binutils-make.log

– Manually change documentation location.

• GCC





· <ghostscript executables>

* /usr/local/bin

* /usr/bin

* /bin

* /mingw/bin

* c:/cygwin/bin


LDFLAGS=’-L /usr/local/lib -R /usr/local/lib’ \CFLAGS=’-D__USE_MINGW_ACCESS’ \../gcc-$version/configure \

--with-gmp=/usr/local \--with-mpfr=/usr/local \--with-mpc=/usr/local \--prefix=$installdir \--target=$target \--enable-languages=c,c++ \--with-dwarf2 \--enable-doc \--with-docdir=$installdir/doc/$project \



--disable-shared \--disable-libada \--disable-libssp \2>&1 | tee $project-configure.log

– Make

make all html install 2>&1 | tee $package-make.log

• avr-libc

– Open source code package.

– Configure and build at the top of the source code tree.


* /usr/local/bin

* /mingw/bin

* /bin


* <install directory>/bin

* <Doxygen executables>

* <NetPBM executables>

* <fig2dev executable>

* <Ghostscript executables>

* c:/cygwin/bin– Configure

./configure \--host=avr \--prefix=$installdir \--enable-doc \--disable-versioned-doc \--enable-html-doc \--enable-pdf-doc \--enable-man-doc \--mandir=$installdir/man \--datadir=$installdir \2>&1 | tee $package-configure.log

– Make

make all install 2>&1 | tee $package-make.log

– Manually change location of man page documentation.

– Move the examples to the top level of the install tree.

– Convert line endings in examples to Windows line endings.

– Convert line endings in header files to Windows line endings.

• AVRDUDE





* /usr/local/bin

* /usr/bin


80 CONTENTS

* /bin

* /mingw/bin

* c:/cygwin/bin

* <install directory>/bin– Set location of LibUSB headers and libraries

export CPPFLAGS="-I../../libusb-win32-device-bin-$libusb_version/include"export CFLAGS="-I../../libusb-win32-device-bin-$libusb_version/include"export LDFLAGS="-L../../libusb-win32-device-bin-$libusb_version/lib/gcc"

– Configure

./configure \--prefix=$installdir \--datadir=$installdir \--sysconfdir=$installdir/bin \--enable-doc \--disable-versioned-doc \2>&1 | tee $package-configure.log

– Make

make -k all install 2>&1 | tee $package-make.log

– Convert line endings in avrdude config file to Windows line endings.

– Delete backup copy of avrdude config file in install directory if exists.

• Insight/GDB





* /usr/local/bin

* /usr/bin

* /bin

* /mingw/bin

* c:/cygwin/bin


CFLAGS=-D__USE_MINGW_ACCESS \LDFLAGS=’-static’ \../$archivedir/configure \

--prefix=$installdir \--target=avr \--with-gmp=/usr/local \--with-mpfr=/usr/local \--enable-doc \2>&1 | tee insight-configure.log

– Make


• SRecord







* /usr/local/bin

* /usr/bin

* /bin

* /mingw/bin

* c:/cygwin/bin


./configure \--prefix=$installdir \--infodir=$installdir/info \--mandir=$installdir/man \2>&1 | tee $package-configure.log

– Make


Build the tools below in Cygwin.

• AVaRICE





* /usr/local/bin

* /usr/bin

* /bin

* <install directory>/bin– Set location of LibUSB headers and libraries

export CPPFLAGS=-I$startdir/libusb-win32-device-bin-$libusb_version/includeexport CFLAGS=-I$startdir/libusb-win32-device-bin-$libusb_version/includeexport LDFLAGS="-static -L$startdir/libusb-win32-device-bin-$libusb_version/lib/gcc "

– Configure

../$archivedir/configure \--prefix=$installdir \--datadir=$installdir/doc \--mandir=$installdir/man \--infodir=$installdir/info \2>&1 | tee avarice-configure.log

– Make

make all install 2>&1 | tee avarice-make.log

• SimulAVR






82 CONTENTS

* /usr/local/bin

* /usr/bin

* /bin


export LDFLAGS="-static"../$archivedir/configure \

--prefix=$installdir \--datadir=$installdir \--disable-tests \--disable-versioned-doc \2>&1 | tee simulavr-configure.log

– Make

make -k all install 2>&1 | tee simulavr-make.logmake pdf install-pdf 2>&1 | tee simulavr-pdf-make.log

13 Using the GNU tools

This is a short summary of the AVR-specific aspects of using the GNU tools. Normally, the generic documentation ofthese tools is fairly large and maintained in texinfo files. Command-line options are explained in detail in the manualpage.

13.1 Options for the C compiler avr-gcc

13.1.1 Machine-specific options for the AVR

The following machine-specific options are recognized by the C compiler frontend. In addition to the preprocessormacros indicated in the tables below, the preprocessor will define the macros AVR and __AVR (to the value 1) whencompiling for an AVR target. The macro AVR will be defined as well when using the standard levels gnu89 (default) andgnu99 but not with c89 and c99.

• -mmcu=architecture

Compile code for architecture. Currently known architectures are

Architecture PBSMacros PBSDescriptionavr1 PBSAVR_ARCH=1

AVR_ASM_ONLYAVR_2_BYTE_PC [2]

PBSSimple CPU core,only assembler support

avr2 PBSAVR_ARCH=2AVR_2_BYTE_PC [2]

PBS"Classic" CPU core,up to 8 KB of ROM

avr25 [1] PBSAVR_ARCH=25AVR_HAVE_MOVW [1]AVR_HAVE_LPMX [1]AVR_2_BYTE_PC [2]

PBS"Classic" CPU corewith ’MOVW’ and ’LPMRx, Z[+]’ instruction, upto 8 KB of ROM

avr3 PBSAVR_ARCH=3AVR_MEGA [5]AVR_HAVE_JMP_CALL [4]AVR_2_BYTE_PC [2]

PBS"Classic" CPU core,16 KB to 64 KB of ROM


13.1 Options for the C compiler avr-gcc 83

avr31 PBSAVR_ARCH=31AVR_MEGA [5]AVR_HAVE_JMP_CALL [4]AVR_HAVE_RAMPZ [4]AVR_HAVE_ELPM [4]AVR_2_BYTE_PC [2]

PBS"Classic" CPU core,128 KB of ROM

avr35 [3] PBSAVR_ARCH=35AVR_MEGA [5]AVR_HAVE_JMP_CALL [4]AVR_HAVE_MOVW [1]AVR_HAVE_LPMX [1]AVR_2_BYTE_PC [2]

PBS"Classic" CPU corewith ’MOVW’ and ’LPMRx, Z[+]’ instruction, 16KB to 64 KB of ROM

avr4 PBSAVR_ARCH=4AVR_ENHANCED [5]AVR_HAVE_MOVW [1]AVR_HAVE_LPMX [1]AVR_HAVE_MUL [1]AVR_2_BYTE_PC [2]

PBS"Enhanced" CPUcore, up to 8 KB of ROM

avr5 PBSAVR_ARCH=5AVR_MEGA [5]AVR_ENHANCED [5]AVR_HAVE_JMP_CALL [4]AVR_HAVE_MOVW [1]AVR_HAVE_LPMX [1]AVR_HAVE_MUL [1]AVR_2_BYTE_PC [2]

PBS"Enhanced" CPUcore, 16 KB to 64 KB ofROM

avr51 PBSAVR_ARCH=51AVR_MEGA [5]AVR_ENHANCED [5]AVR_HAVE_JMP_CALL [4]AVR_HAVE_MOVW [1]AVR_HAVE_LPMX [1]AVR_HAVE_MUL [1]AVR_HAVE_RAMPZ [4]AVR_HAVE_ELPM [4]AVR_HAVE_ELPMX [4]AVR_2_BYTE_PC [2]

PBS"Enhanced" CPUcore, 128 KB of ROM

avr6 [2] PBSAVR_ARCH=6AVR_MEGA [5]AVR_ENHANCED [5]AVR_HAVE_JMP_CALL [4]AVR_HAVE_MOVW [1]AVR_HAVE_LPMX [1]AVR_HAVE_MUL [1]AVR_HAVE_RAMPZ [4]AVR_HAVE_ELPM [4]AVR_HAVE_ELPMX [4]AVR_3_BYTE_PC [2]

PBS"Enhanced" CPUcore, 256 KB of ROM

[1] New in GCC 4.2[2] Unofficial patch for GCC 4.1[3] New in GCC 4.2.3[4] New in GCC 4.3[5] Obsolete.


84 CONTENTS

By default, code is generated for the avr2 architecture.

Note that when only using -mmcu=architecture but no -mmcu=MCU type, including the file <avr/io.h> cannotwork since it cannot decide which device’s definitions to select.

• -mmcu=MCU type

The following MCU types are currently understood by avr-gcc. The table matches them against the correspondingavr-gcc architecture name, and shows the preprocessor symbol declared by the -mmcu option.

Architecture PBSMCU name PBSMacro

avr1 PBSat90s1200 PBS__AVR_AT90←↩S1200__

avr1 PBSattiny11 PBS__AVR_ATtiny11←↩__














avr2 PBSat90c8534 PBS__AVR_AT90←↩C8534__


avr2/avr25 [1] PBSat86rf401 PBS__AVR_AT86R←↩F401__

avr2/avr25 [1] PBSata5272 PBS__AVR_ATA5272←↩__

avr2/avr25 [1] PBSattiny13 PBS__AVR_ATtiny13←↩__



avr2/avr25 [1] PBSattiny13a PBS__AVR_ATtiny13←↩A__

avr2/avr25 [1] PBSattiny2313 PBS__AVR_A←↩Ttiny2313__

avr2/avr25 [1] PBSattiny2313a PBS__AVR_A←↩Ttiny2313A__







avr2/avr25 [1] PBSattiny43u PBS__AVR_ATtiny43←↩U__















avr3 PBSatmega603 PBS__AVR_A←↩Tmega603__

avr3 PBSat43usb355 PBS__AVR_AT43US←↩B355__


86 CONTENTS

avr3/avr31 [3] PBSatmega103 PBS__AVR_A←↩Tmega103__

avr3/avr31 [3] PBSat43usb320 PBS__AVR_AT43US←↩B320__



avr3/avr35 [2] PBSata5505 PBS__AVR_ATA5505←↩__

avr3/avr35 [2] PBSatmega8u2 PBS__AVR_ATmega8←↩U2__

avr3/avr35 [2] PBSatmega16u2 PBS__AVR_A←↩Tmega16U2__

avr3/avr35 [2] PBSatmega32u2 PBS__AVR_A←↩Tmega32U2__



avr3 PBSat76c711 PBS__AVR_AT76←↩C711__

avr4 PBSata6285 PBS__AVR_ATA6285←↩__




avr4 PBSatmega48a PBS__AVR_A←↩Tmega48A__

avr4 PBSatmega48pa PBS__AVR_A←↩Tmega48PA__

avr4 PBSatmega48p PBS__AVR_A←↩Tmega48P__

avr4 PBSatmega8 PBS__AVR_ATmega8←↩__

avr4 PBSatmega8a PBS__AVR_ATmega8←↩A__









avr4 PBSatmega8hva PBS__AVR_ATmega8←↩HVA__

avr4 PBSat90pwm1 PBS__AVR_AT90PW←↩M1__


avr4 PBSat90pwm2b PBS__AVR_AT90PW←↩M2B__


avr4 PBSat90pwm3b PBS__AVR_AT90PW←↩M3B__


avr5 PBSat90can32 PBS__AVR_AT90CA←↩N32__

avr5 PBSat90can64 PBS__AVR_AT90CA←↩N64__




avr5 PBSat90scr100 PBS__AVR_AT90SC←↩R100__



avr5 PBSat94k PBS__AVR_AT94K__avr5 PBSatmega16 PBS__AVR_A←↩

Tmega16__avr5 PBSata5790 PBS__AVR_ATA5790←↩

__avr5 PBSata5795 PBS__AVR_ATA5795←↩

__avr5 PBSatmega161 PBS__AVR_A←↩

Tmega161__avr5 PBSatmega162 PBS__AVR_A←↩

Tmega162__avr5 PBSatmega163 PBS__AVR_A←↩

Tmega163__avr5 PBSatmega164a PBS__AVR_A←↩

Tmega164A__avr5 PBSatmega164p PBS__AVR_A←↩

Tmega164P__avr5 PBSatmega164pa PBS__AVR_A←↩

Tmega164PA__avr5 PBSatmega165 PBS__AVR_A←↩

Tmega165__avr5 PBSatmega165a PBS__AVR_A←↩

Tmega165A__


88 CONTENTS












avr5 PBSatmega16hva PBS__AVR_A←↩Tmega16HVA__

avr5 PBSatmega16hva2 PBS__AVR_A←↩Tmega16HVA2__

avr5 PBSatmega16hvb PBS__AVR_A←↩Tmega16HVB__

avr5 PBSatmega16hvbrevb PBS__AVR_A←↩Tmega16HVBREVB__

avr5 PBSatmega16m1 PBS__AVR_A←↩Tmega16M1__

avr5 PBSatmega16u4 PBS__AVR_A←↩Tmega16U4__



























avr5 PBSatmega32c1 PBS__AVR_A←↩Tmega32C1__

avr5 PBSatmega32hvb PBS__AVR_A←↩Tmega32HVB__

avr5 PBSatmega32hvbrevb PBS__AVR_A←↩Tmega32HVBREVB__





avr5 PBSatmega644rfr2 PBS__AVR_A←↩Tmega644RFR2__







90 CONTENTS
















avr5 PBSatmega64c1 PBS__AVR_A←↩Tmega64C1__

avr5 PBSatmega64hve PBS__AVR_A←↩Tmega64HVE__


avr5 PBSm3000 PBS__AVR_M3000__

avr5/avr51 [3] PBSat90can128 PBS__AVR_AT90CA←↩N128__




avr5/avr51 [3] PBSatmega128a PBS__AVR_A←↩Tmega128A__






avr5/avr51 [3] PBSatmega1284p PBS__AVR_A←↩Tmega1284P__

avr5/avr51 [3] PBSatmega1284rfr2 PBS__AVR_A←↩Tmega1284RFR2__

avr5/avr51 [3] PBSatmega128rfr2 PBS__AVR_A←↩Tmega128RFR2__





avrxmega2 PBSatxmega16a4 PBS__AVR_A←↩Txmega16A4__

avrxmega2 PBSatxmega16a4u PBS__AVR_A←↩Txmega16A4U__

avrxmega2 PBSatxmega16c4 PBS__AVR_A←↩Txmega16C4__

avrxmega2 PBSatxmega16d4 PBS__AVR_A←↩Txmega16D4__








avrxmega4 PBSatxmega64b1 PBS__AVR_A←↩Txmega64B1__







92 CONTENTS















avrxmega6 PBSatxmega256a3b PBS__AVR_A←↩Txmega256A3B__

avrxmega6 PBSatxmega256a3bu PBS__AVR_A←↩Txmega256A3BU__








avrtiny10 PBSattiny4 PBS__AVR_ATtiny4_←↩_





avrtiny10 PBSattiny10 PBS__AVR_ATtiny10←↩__



[1] ’avr25’ architecture is new in GCC 4.2[2] ’avr35’ architecture is new in GCC 4.2.3[3] ’avr31’ and ’avr51’ architectures is new in GCC 4.3

• -morder1

• -morder2

Change the order of register assignment. The default is

r24, r25, r18, r19, r20, r21, r22, r23, r30, r31, r26, r27, r28, r29, r17, r16, r15, r14, r13, r12, r11, r10, r9, r8, r7, r6, r5, r4,r3, r2, r0, r1

Order 1 uses


Order 2 uses


• -mint8

Assume int to be an 8-bit integer. Note that this is not really supported by avr-libc, so it should normally not beused. The default is to use 16-bit integers.

• -mno-interrupts

Generates code that changes the stack pointer without disabling interrupts. Normally, the state of the status registerSREG is saved in a temporary register, interrupts are disabled while changing the stack pointer, and SREG is restored.

Specifying this option will define the preprocessor macro NO_INTERRUPTS to the value 1.

• -mcall-prologues

Use subroutines for function prologue/epilogue. For complex functions that use many registers (that needs to besaved/restored on function entry/exit), this saves some space at the cost of a slightly increased execution time.

• -mtiny-stack

Change only the low 8 bits of the stack pointer.

• -mno-tablejump


94 CONTENTS

Deprecated, use -fno-jump-tables instead.

• -mshort-calls

Use rjmp/rcall (limited range) on >8K devices. On avr2 and avr4 architectures (less than 8 KB or flash mem-ory), this is always the case. On avr3 and avr5 architectures, calls and jumps to targets outside the current functionwill by default use jmp/call instructions that can cover the entire address range, but that require more flash ROMand execution time.

• -mrtl

Dump the internal compilation result called "RTL" into comments in the generated assembler code. Used for debuggingavr-gcc.

• -msize

Dump the address, size, and relative cost of each statement into comments in the generated assembler code. Used fordebugging avr-gcc.

• -mdeb

Generate lots of debugging information to stderr.

13.1.2 Selected general compiler options

The following general gcc options might be of some interest to AVR users.

• -On

Optimization level n. Increasing n is meant to optimize more, an optimization level of 0 means no optimization at all,which is the default if no -O option is present. The special option -Os is meant to turn on all -O2 optimizations that arenot expected to increase code size.

Note that at -O3, gcc attempts to inline all "simple" functions. For the AVR target, this will normally constitute a large pes-simization due to the code increasement. The only other optimization turned on with -O3 is -frename-registers,which could rather be enabled manually instead.

A simple -O option is equivalent to -O1.

Note also that turning off all optimizations will prevent some warnings from being issued since the generation of thosewarnings depends on code analysis steps that are only performed when optimizing (unreachable code, unused vari-ables).

See also the appropriate FAQ entry for issues regarding debugging optimized code.

• -Wa,assembler-options

• -Wl,linker-options

Pass the listed options to the assembler, or linker, respectively.

• -g


13.2 Options for the assembler avr-as 95

Generate debugging information that can be used by avr-gdb.

• -ffreestanding

Assume a "freestanding" environment as per the C standard. This turns off automatic builtin functions (though they canstill be reached by prepending __builtin_ to the actual function name). It also makes the compiler not complainwhen main() is declared with a void return type which makes some sense in a microcontroller environment wherethe application cannot meaningfully provide a return value to its environment (in most cases, main() won’t even returnanyway). However, this also turns off all optimizations normally done by the compiler which assume that functions knownby a certain name behave as described by the standard. E. g., applying the function strlen() to a literal string will normallycause the compiler to immediately replace that call by the actual length of the string, while with -ffreestanding, itwill always call strlen() at run-time.

• -funsigned-char

Make any unqualfied char type an unsigned char. Without this option, they default to a signed char.

• -funsigned-bitfields

Make any unqualified bitfield type unsigned. By default, they are signed.

• -fshort-enums

Allocate to an enum type only as many bytes as it needs for the declared range of possible values. Specifically, theenum type will be equivalent to the smallest integer type which has enough room.

• -fpack-struct

Pack all structure members together without holes.

• -fno-jump-tables

Do not generate tablejump instructions. By default, jump tables can be used to optimize switch statements. Whenturned off, sequences of compare statements are used instead. Jump tables are usually faster to execute on average,but in particular for switch statements, where most of the jumps would go to the default label, they might waste a bitof flash memory.

NOTE: The tablejump instructions use the LPM assembler instruction for access to jump tables. Always use-fno-jump-tables switch, if compiling a bootloader for devices with more than 64 KB of code memory.

13.2 Options for the assembler avr-as

13.2.1 Machine-specific assembler options

• -mmcu=architecture

• -mmcu=MCU name

avr-as understands the same -mmcu= options as avr-gcc. By default, avr2 is assumed, but this can be altered by usingthe appropriate .arch pseudo-instruction inside the assembler source file.


96 CONTENTS

• -mall-opcodes

Turns off opcode checking for the actual MCU type, and allows any possible AVR opcode to be assembled.

• -mno-skip-bug

Don’t emit a warning when trying to skip a 2-word instruction with a CPSE/SBIC/SBIS/SBRC/SBRS instruction.Early AVR devices suffered from a hardware bug where these instructions could not be properly skipped.

• -mno-wrap

For RJMP/RCALL instructions, don’t allow the target address to wrap around for devices that have more than 8 KB ofmemory.

• -gstabs

Generate .stabs debugging symbols for assembler source lines. This enables avr-gdb to trace through assembler sourcefiles. This option must not be used when assembling sources that have been generated by the C compiler; these filesalready contain the appropriate line number information from the C source files.

• -a[cdhlmns=file]

Turn on the assembler listing. The sub-options are:

• c omit false conditionals

• d omit debugging directives

• h include high-level source

• l include assembly

• m include macro expansions

• n omit forms processing

• s include symbols

• =file set the name of the listing file

The various sub-options can be combined into a single -a option list; =file must be the last one in that case.

13.2.2 Examples for assembler options passed through the C compiler

Remember that assembler options can be passed from the C compiler frontend using -Wa (see above), so in order toinclude the C source code into the assembler listing in file foo.lst, when compiling foo.c, the following compilercommand-line can be used:

$ avr-gcc -c -O foo.c -o foo.o -Wa,-ahls=foo.lst

In order to pass an assembler file through the C preprocessor first, and have the assembler generate line numberdebugging information for it, the following command can be used:

$ avr-gcc -c -x assembler-with-cpp -o foo.o foo.S -Wa,--gstabs

Note that on Unix systems that have case-distinguishing file systems, specifying a file name with the suffix .S (upper-case letter S) will make the compiler automatically assume -x assembler-with-cpp, while using .s would passthe file directly to the assembler (no preprocessing done).


13.3 Controlling the linker avr-ld 97

13.3 Controlling the linker avr-ld

13.3.1 Selected linker options

While there are no machine-specific options for avr-ld, a number of the standard options might be of interest to AVRusers.

• -lname

Locate the archive library named libname.a, and use it to resolve currently unresolved symbols from it. The libraryis searched along a path that consists of builtin pathname entries that have been specified at compile time (e. g./usr/local/avr/lib on Unix systems), possibly extended by pathname entries as specified by -L options (thatmust precede the -l options on the command-line).

• -Lpath

Additional location to look for archive libraries requested by -l options.

• -defsym symbol=expr

Define a global symbol symbol using expr as the value.

• -M

Print a linker map to stdout.

• -Map mapfile

Print a linker map to mapfile.

• -cref

Output a cross reference table to the map file (in case -Map is also present), or to stdout.

• -section-start sectionname=org

Start section sectionname at absolute address org.

• -Tbss org

• -Tdata org

• -Ttext org

Start the bss, data, or text section at org, respectively.

• -T scriptfile

Use scriptfile as the linker script, replacing the default linker script. Default linker scripts are stored in a system-specificlocation (e. g. under /usr/local/avr/lib/ldscripts on Unix systems), and consist of the AVR architecturename (avr2 through avr5) with the suffix .x appended. They describe how the various memory sections will be linkedtogether.


98 CONTENTS

13.3.2 Passing linker options from the C compiler

By default, all unknown non-option arguments on the avr-gcc command-line (i. e., all filename arguments that don’thave a suffix that is handled by avr-gcc) are passed straight to the linker. Thus, all files ending in .o (object files) and .a(object libraries) are provided to the linker.

System libraries are usually not passed by their explicit filename but rather using the -l option which uses an abbre-viated form of the archive filename (see above). avr-libc ships two system libraries, libc.a, and libm.a. Whilethe standard library libc.a will always be searched for unresolved references when the linker is started using the Ccompiler frontend (i. e., there’s always at least one implied -lc option), the mathematics library libm.a needs to beexplicitly requested using -lm. See also the entry in the FAQ explaining this.

Conventionally, Makefiles use the make macro LDLIBS to keep track of -l (and possibly -L) options that should onlybe appended to the C compiler command-line when linking the final binary. In contrast, the macro LDFLAGS is usedto store other command-line options to the C compiler that should be passed as options during the linking stage. Thedifference is that options are placed early on the command-line, while libraries are put at the end since they are to beused to resolve global symbols that are still unresolved at this point.

Specific linker flags can be passed from the C compiler command-line using the -Wl compiler option, see above. Thisoption requires that there be no spaces in the appended linker option, while some of the linker options above (like -Mapor -defsym) would require a space. In these situations, the space can be replaced by an equal sign as well. Forexample, the following command-line can be used to compile foo.c into an executable, and also produce a link mapthat contains a cross-reference list in the file foo.map:

$ avr-gcc -O -o foo.out -Wl,-Map=foo.map -Wl,--cref foo.c

Alternatively, a comma as a placeholder will be replaced by a space before passing the option to the linker. So for adevice with external SRAM, the following command-line would cause the linker to place the data segment at address0x2000 in the SRAM:

$ avr-gcc -mmcu=atmega128 -o foo.out -Wl,-Tdata,0x802000

See the explanation of the data section for why 0x800000 needs to be added to the actual value. Note that the stackwill still remain in internal RAM, through the symbol __stack that is provided by the run-time startup code. This isprobably a good idea anyway (since internal RAM access is faster), and even required for some early devices that hadhardware bugs preventing them from using a stack in external RAM. Note also that the heap for malloc() will still beplaced after all the variables in the data section, so in this situation, no stack/heap collision can occur.

In order to relocate the stack from its default location at the top of interns RAM, the value of the symbol __stack canbe changed on the linker command-line. As the linker is typically called from the compiler frontend, this can be achievedusing a compiler option like

-Wl,--defsym=__stack=0x8003ff

The above will make the code use stack space from RAM address 0x3ff downwards. The amount of stack spaceavailable then depends on the bottom address of internal RAM for a particular device. It is the responsibility of theapplication to ensure the stack does not grow out of bounds, as well as to arrange for the stack to not collide withvariable allocations made by the compiler (sections .data and .bss).

14 Compiler optimization

14.1 Problems with reordering code


14.1 Problems with reordering code 99

Author

Jan Waclawek

Programs contain sequences of statements, and a naive compiler would execute them exactly in the order as they arewritten. But an optimizing compiler is free to reorder the statements - or even parts of them - if the resulting "net effect"is the same. The "measure" of the "net effect" is what the standard calls "side effects", and is accomplished exclusivelythrough accesses (reads and writes) to variables qualified as volatile. So, as long as all volatile reads and writesare to the same addresses and in the same order (and writes write the same values), the program is correct, regardlessof other operations in it. (One important point to note here is, that time duration between consecutive volatile accessesis not considered at all.)

Unfortunately, there are also operations which are not covered by volatile accesses. An example of this in avr-gcc/avr-libcare the cli() and sei() macros defined in <avr/interrupt.h>, which convert directly to the respective assembler mnemonicsthrough the asm() statement. These don’t constitute a variable access at all, not even volatile, so the compiler is freeto move them around. Although there is a "volatile" qualifier which can be attached to the asm() statement, its effect on(re)ordering is not clear from the documentation (and is more likely only to prevent complete removal by the optimiser),as it (among other) states:

Note that even a volatile asm instruction can be moved relative to other code, including across jump instructions. [...]Similarly, you can’t expect a sequence of volatile asm instructions to remain perfectly consecutive.

See also

http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Extended-Asm.html

There is another mechanism which can be used to achieve something similar: memory barriers. This is accomplishedthrough adding a special "memory" clobber to the inline asm statement, and ensures that all variables are flushed fromregisters to memory before the statement, and then re-read after the statement. The purpose of memory barriers isslightly different than to enforce code ordering: it is supposed to ensure that there are no variables "cached" in registers,so that it is safe to change the content of registers e.g. when switching context in a multitasking OS (on "big" processorswith out-of-order execution they also imply usage of special instructions which force the processor into "in-order" state(this is not the case of AVRs)).

However, memory barrier works well in ensuring that all volatile accesses before and after the barrier occur in the givenorder with respect to the barrier. However, it does not ensure the compiler moving non-volatile-related statements acrossthe barrier. Peter Dannegger provided a nice example of this effect:

#define cli() __asm volatile( "cli" ::: "memory" )#define sei() __asm volatile( "sei" ::: "memory" )

unsigned int ivar;

void test2( unsigned int val ){

val = 65535U / val;

cli();

ivar = val;

sei();}

compiles with optimisations switched on (-Os) to

00000112 <test2>:112: bc 01 movw r22, r24114: f8 94 cli116: 8f ef ldi r24, 0xFF ; 255118: 9f ef ldi r25, 0xFF ; 25511a: 0e 94 96 00 call 0x12c ; 0x12c <__udivmodhi4>


http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Extended-Asm.html

100 CONTENTS

11e: 70 93 01 02 sts 0x0201, r23122: 60 93 00 02 sts 0x0200, r22126: 78 94 sei128: 08 95 ret

where the potentially slow division is moved across cli(), resulting in interrupts to be disabled longer than intended.Note, that the volatile access occurs in order with respect to cli() or sei(); so the "net effect" required by the standardis achieved as intended, it is "only" the timing which is off. However, for most of embedded applications, timing is animportant, sometimes critical factor.

See also

https://www.mikrocontroller.net/topic/65923

Unfortunately, at the moment, in avr-gcc (nor in the C standard), there is no mechanism to enforce complete match ofwritten and executed code ordering - except maybe of switching the optimization completely off (-O0), or writing all thecritical code in assembly.

To sum it up:

• memory barriers ensure proper ordering of volatile accesses

• memory barriers don’t ensure statements with no volatile accesses to be reordered across the barrier

15 Using the avrdude program

Note

This section was contributed by Brian Dean [ [email protected] ].The avrdude program was previously called avrprog. The name was changed to avoid confusion with the avrprogprogram that Atmel ships with AvrStudio.

avrdude is a program that is used to update or read the flash and EEPROM memories of Atmel AVR microcontrollerson FreeBSD Unix. It supports the Atmel serial programming protocol using the PC’s parallel port and can upload eithera raw binary file or an Intel Hex format file. It can also be used in an interactive mode to individually update EEPROMcells, fuse bits, and/or lock bits (if their access is supported by the Atmel serial programming protocol.) The main flashinstruction memory of the AVR can also be programmed in interactive mode, however this is not very useful becauseone can only turn bits off. The only way to turn flash bits on is to erase the entire memory (using avrdude’s -e option).

avrdude is part of the FreeBSD ports system. To install it, simply do the following:

# cd /usr/ports/devel/avrdude# make install

Once installed, avrdude can program processors using the contents of the .hex file specified on the command line. Inthis example, the file main.hex is burned into the flash memory:

# avrdude -p 2313 -e -m flash -i main.hex

avrdude: AVR device initialized and ready to accept instructions

avrdude: Device signature = 0x1e9101

avrdude: erasing chipavrdude: done.avrdude: reading input file "main.hex"


https://www.mikrocontroller.net/topic/65923

mailto:[email protected]

16 Release Numbering and Methodology 101

avrdude: input file main.hex auto detected as Intel Hex

avrdude: writing flash:1749 0x00avrdude: 1750 bytes of flash writtenavrdude: verifying flash memory against main.hex:avrdude: reading on-chip flash data:1749 0x00avrdude: verifying ...avrdude: 1750 bytes of flash verified

avrdude done. Thank you.

The -p 2313 option lets avrdude know that we are operating on an AT90S2313 chip. This option spec-ifies the device id and is matched up with the device of the same id in avrdude’s configuration file (/usr/local/etc/avrdude.conf ). To list valid parts, specify the -v option. The -e option instructs avrdudeto perform a chip-erase before programming; this is almost always necessary before programming the flash. The -mflash option indicates that we want to upload data into the flash memory, while -i main.hex specifies the nameof the input file.

The EEPROM is uploaded in the same way, the only difference is that you would use -m eeprom instead of -mflash.

To use interactive mode, use the -t option:

# avrdude -p 2313 -tavrdude: AVR device initialized and ready to accept instructionsavrdude: Device signature = 0x1e9101avrdude>

The ’?’ command displays a list of validcommands:

avrdude> ?>>> ?Valid commands:

dump : dump memory : dump <memtype> <addr> <N-Bytes>read : alias for dumpwrite : write memory : write <memtype> <addr> <b1> <b2> ... <bN>erase : perform a chip erasesig : display device signature bytespart : display the current part informationsend : send a raw command : send <b1> <b2> <b3> <b4>help : help? : helpquit : quit

Use the ’part’ command to display valid memory types for use with the’dump’ and ’write’ commands.

avrdude>

16 Release Numbering and Methodology

16.1 Release Version Numbering Scheme

Release numbers consist of three parts, a major number, a minor number, and a revision number, each separated by adot.

The major number is currently 1 (and has always been). It will only be bumped in case a new version offers a majorchange in the API that is not backwards compatible.


102 CONTENTS

In the past (up to 1.6.x), even minor numbers have been used to indicate "stable" releases, and odd minor numbers havebeen reserved for development branches/versions. As the latter has never really been used, and maintaining a stablebranch that eventually became effectively the same as the development version has proven to be just a cumbersomeand tedious job, this scheme has given up in early 2010, so starting with 1.7.0, every minor number will be used. Minornumbers will be bumped upon judgement of the development team, whenever it seems appropriate, but at least in caseswhere some API was changed.

Starting with version 1.4.0, a file <avr/version.h> indicates the library version of an installed library tree.

16.2 Releasing AVR Libc

The information in this section is only relevant to AVR Libc developers and can be ignored by end users.

Note

In what follows, I assume you know how to use SVN and how to checkout multiple source trees in a singledirectory without having them clobber each other. If you don’t know how to do this, you probably shouldn’t bemaking releases or cutting branches.

16.2.1 Creating an SVN branch

The following steps should be taken to cut a branch in SVN (assuming $username is set to your savannah username):

1. Check out a fresh source tree from SVN trunk.

2. Update the NEWS file with pending release number and commit to SVN trunk:Change Changes since avr-libc-<last_release>: to Changes in avr-libc-<this_relelase>.

3. Set the branch-point tag (setting <major> and <minor> accordingly):svn copy svn+ssh://[email protected]/avr-libc/trunk svn+ssh←↩://[email protected]/avr-libc/tags/avr-libc-<major>_<minor>-branchpoint

4. Create the branch:svn copy svn+ssh://[email protected]/avr-libc/trunk svn+ssh←↩://[email protected]/avr-libc/branches/avr-libc-<major>_←↩<minor>-branch

5. Update the package version in configure.ac and commit configure.ac to SVN trunk:Change minor number to next odd value.

6. Update the NEWS file and commit to SVN trunk:Add Changes since avr-libc-<this_release>:

7. Check out a new tree for the branch:svn co svn+ssh://[email protected]/avr-libc/branches/avr-libc-<major>←↩_<minor>-branch

8. Update the package version in configure.ac and commit configure.ac to SVN branch:Change the patch number to 90 to denote that this now a branch leading up to a release. Be sure to leave the<date> part of the version.

9. Bring the build system up to date by running bootstrap and configure.

10. Perform a ’make distcheck’ and make sure it succeeds. This will create the snapshot source tarball. This shouldbe considered the first release candidate.

11. Upload the snapshot tarball to savannah.


16.2 Releasing AVR Libc 103

12. Update the bug tracker interface on Savannah: Bugs —> Edit field values —> Release / Fixed Release

13. Announce the branch and the branch tag to the avr-libc-dev list so other developers can checkout the branch.

16.2.2 Making a release

A stable release will only be done on a branch, not from the SVN trunk.

The following steps should be taken when making a release:

1. Make sure the source tree you are working from is on the correct branch:svn switch svn+ssh://[email protected]/avr-libc/branches/avr-libc-<major>←↩_<minor>-branch

2. Update the package version in configure.ac and commit it to SVN.

3. Update the gnu tool chain version requirements in the README and commit to SVN.

4. Update the ChangeLog file to note the release and commit to SVN on the branch:Add Released avr-libc-<this_release>.

5. Update the NEWS file with pending release number and commit to SVN:Change Changes since avr-libc-<last_release>: to Changes in avr-libc-<this_relelase>:.

6. Bring the build system up to date by running bootstrap and configure.

7. Perform a ’make distcheck’ and make sure it succeeds. This will create the source tarball.

8. Tag the release:svn copy . svn+ssh://[email protected]/avr-libc/tags/avr-libc-<major>←↩_<minor>_<patch>-releaseorsvn copy svn+ssh://[email protected]/avr-libc/branches/avr-libc-<major>←↩_<minor>-branch svn+ssh://[email protected]/avr-libc/tags/avr-libc-<major>←↩_<minor>_<patch>-release

9. Upload the tarball to savannah.

10. Update the NEWS file, and commit to SVN:Add Changes since avr-libc-<major>_<minor>_<patch>:

11. Update the bug tracker interface on Savannah: Bugs —> Edit field values —> Release / Fixed Release

12. Generate the latest documentation and upload to savannah.

13. Announce the release.

The following hypothetical diagram should help clarify version and branch relationships.


104 CONTENTS

cvs tag avr−libc−1_0_1−release

cvs tag −b avr−libc−1_0−branch

cvs tag avr−libc−1_0−branchpoint

set version to 1.1.0.<date>


set version to 1.0

cvs tag avr−libc−1_0−release

1.2 Branch1.0 BranchHEAD


cvs tag avr−libc−1_2−branchpoint

cvs tag avr−libc−2.0−branchpoint

cvs tag −b avr−libc−1_2−branchset version to 1.3.0.<date>



set version to 1.0.1

set version to 1.2

cvs tag avr−libc−1_2−release

Figure 4: Release tree

17 Acknowledgments

This document tries to tie together the labors of a large group of people. Without these individuals’ efforts, we wouldn’thave a terrific, free set of tools to develop AVR projects. We all owe thanks to:

- The GCC Team, which produced a very capable set of development tools foran amazing number of platforms and processors.

- Denis Chertykov [ [email protected] ] for making the AVR-specific changesto the GNU tools.

- Denis Chertykov and Marek Michalkiewicz [ [email protected] ] fordeveloping the standard libraries and startup code for \b AVR-GCC.

- Uros Platise for developing the AVR programmer tool, \b uisp.

- Joerg Wunsch [ [email protected] ] for adding all the AVR developmenttools to the FreeBSD [ http://www.freebsd.org ] ports tree and forproviding the basics for the \ref demo_project "demo project".

- Brian Dean [ [email protected] ] for developing \b avrdude (an alternativeto <b>uisp</b>) and for contributing \ref using_avrprog "documentation"which describes how to use it. \b Avrdude was previously called\b avrprog.

- Eric Weddington [ [email protected] ] for maintaining the \b WinAVRpackage and thus making the continued improvements to theopen source AVR toolchain available to many users.


18 Todo List 105

- Rich Neswold for writing the original avr-tools document (which hegraciously allowed to be merged into this document) and hisimprovements to the \ref demo_project "demo project".

- Theodore A. Roth for having been a long-time maintainer ofmany of the tools (\b AVR-Libc, the AVR port of \b GDB, \b AVaRICE,\b uisp, \b avrdude).

- All the people who currently maintain the tools, and/orhave submitted suggestions, patches and bug reports.

(See the AUTHORS files of the various tools.)

- And lastly, all the users who use the software. If nobody used thesoftware, we would probably not be very motivated to continue to developit. Keep those bug reports coming. ;-)

18 Todo List

Group avr_boot

From email with Marek: On smaller devices (all except ATmega64/128), __SPM_REG is in the I/O space, accessiblewith the shorter "in" and "out" instructions - since the boot loader has a limited size, this could be an importantoptimization.

19 Deprecated List

Global cbi (port, bit)

Global enable_external_int (mask)

Global inb (port)

Global inp (port)

Global INTERRUPT (signame)

Global ISR_ALIAS (vector, target_vector)

For new code, the use of ISR(..., ISR_ALIASOF(...)) is recommended.

Global outb (port, val)

Global outp (val, port)

Global sbi (port, bit)

Global SIGNAL (vector)

Do not use SIGNAL() in new code. Use ISR() instead.

Global timer_enable_int (unsigned char ints)


106 CONTENTS

20 Module Index

20.1 Modules

Here is a list of all modules:

<alloca.h>: Allocate space in the stack 111

<assert.h>: Diagnostics 112

<ctype.h>: Character Operations 113

<errno.h>: System Errors 115

<inttypes.h>: Integer Type conversions 116

<math.h>: Mathematics 127

<setjmp.h>: Non-local goto 137

<stdint.h>: Standard Integer Types 139

<stdio.h>: Standard IO facilities 149

<stdlib.h>: General utilities 163

<string.h>: Strings 172

<time.h>: Time 182

<avr/boot.h>: Bootloader Support Utilities 190

<avr/cpufunc.h>: Special AVR CPU functions 196

<avr/eeprom.h>: EEPROM handling 197

<avr/fuse.h>: Fuse Support 201

<avr/interrupt.h>: Interrupts 204

<avr/io.h>: AVR device-specific IO definitions 222

<avr/lock.h>: Lockbit Support 224

<avr/pgmspace.h>: Program Space Utilities 226

<avr/power.h>: Power Reduction Management 239

<avr/sfr_defs.h>: Special function registers 253

Additional notes from <avr/sfr_defs.h> 252

<avr/signature.h>: Signature Support 255

<avr/sleep.h>: Power Management and Sleep Modes 256

<avr/version.h>: avr-libc version macros 258


21 Data Structure Index 107

<avr/wdt.h>: Watchdog timer handling 260

<util/atomic.h> Atomically and Non-Atomically Executed Code Blocks 263

<util/crc16.h>: CRC Computations 266

<util/delay.h>: Convenience functions for busy-wait delay loops 270

<util/delay_basic.h>: Basic busy-wait delay loops 272

<util/parity.h>: Parity bit generation 273

<util/setbaud.h>: Helper macros for baud rate calculations 274

<util/twi.h>: TWI bit mask definitions 276

<compat/deprecated.h>: Deprecated items 280

<compat/ina90.h>: Compatibility with IAR EWB 3.x 283

Demo projects 284

Combining C and assembly source files 285

A simple project 288

A more sophisticated project 300

Using the standard IO facilities 306

Example using the two-wire interface (TWI) 312

21 Data Structure Index

21.1 Data Structures

Here are the data structures with brief descriptions:

atexit_s 316

div_t 316

ldiv_t 316

tm 317

week_date 318

22 File Index

22.1 File List

Here is a list of all documented files with brief descriptions:


108 CONTENTS

alloca.h ??

assert.h 318

atoi.S 318

atol.S 318

atomic.h 318

boot.h 318

cpufunc.h 323

crc16.h 323

ctype.h 324

defines.h ??

delay.h 324

delay_basic.h 324

deprecated.h ??

dtoa_conv.h ??

eedef.h ??

eeprom.h ??

ephemera_common.h ??

errno.h 325

eu_dst.h ??

fdevopen.c 326

ffs.S 326

ffsl.S 326

ffsll.S 326

fuse.h 326

hd44780.h ??

ina90.h ??

interrupt.h 326

inttypes.h 327

io.h 329

iocompat.h ??


22.1 File List 109

lcd.h ??

lock.h 329

math.h 329

memccpy.S 332

memchr.S 332

memchr_P.S 332

memcmp.S 332

memcmp_P.S 332

memcmp_PF.S 332

memcpy.S 332

memcpy_P.S 332

memmem.S 332

memmove.S 332

memrchr.S 332

memrchr_P.S 332

memset.S 332

parity.h 332

pgmspace.h 332

portpins.h ??

power.h 340

project.h ??

setbaud.h 341

setjmp.h 341

sfr_defs.h ??

signal.h ??

signature.h 341

sleep.h 341

stdint.h 342

stdio.h 344

stdio_private.h ??


110 CONTENTS

stdlib.h 346

stdlib_private.h ??

strcasecmp.S 348

strcasecmp_P.S 348

strcasestr.S 348

strcat.S 348

strcat_P.S 348

strchr.S 348

strchr_P.S 348

strchrnul.S 348

strchrnul_P.S 348

strcmp.S 348

strcmp_P.S 348

strcpy.S 348

strcpy_P.S 348

strcspn.S 348

strcspn_P.S 348

strdup.c 348

string.h 349

strlcat.S 350

strlcat_P.S 350

strlcpy.S 350

strlcpy_P.S 350

strlen.S 350

strlen_P.S 350

strlwr.S 350

strncasecmp.S 350

strncasecmp_P.S 350

strncat.S 350

strncat_P.S 350


22.1 File List 111

strncmp.S 350

strncmp_P.S 350

strncpy.S 350

strncpy_P.S 350

strnlen.S 350

strnlen_P.S 350

strpbrk.S 350

strpbrk_P.S 350

strrchr.S 350

strrchr_P.S 350

strrev.S 350

strsep.S 350

strsep_P.S 350

strspn.S 351

strspn_P.S 351

strstr.S 351

strstr_P.S 351

strtok.c 351

strtok_P.c 351

strtok_r.S 351

strtok_rP.S 351

strupr.S 351

time.h 351

util/twi.h 353

compat/twi.h ??

uart.h ??

usa_dst.h ??

version.h ??

wdt.h 354

xmega.h ??


112 CONTENTS

xtoa_fast.h ??

23 Module Documentation

23.1 <alloca.h>: Allocate space in the stack

Functions

• void ∗ alloca (size_t __size)

23.1.1 Detailed Description

23.1.2 Function Documentation

23.1.2.1 void∗ alloca ( size_t __size )

Allocate __size bytes of space in the stack frame of the caller.

This temporary space is automatically freed when the function that called alloca() returns to its caller. Avr-libc definesthe alloca() as a macro, which is translated into the inlined __builtin_alloca() function. The fact that the codeis inlined, means that it is impossible to take the address of this function, or to change its behaviour by linking with adifferent library.

Returns

alloca() returns a pointer to the beginning of the allocated space. If the allocation causes stack overflow, programbehaviour is undefined.

Warning

Avoid use alloca() inside the list of arguments of a function call.


23.2 <assert.h>: Diagnostics 113

23.2 <assert.h>: Diagnostics

Macros

• #define assert(expression)


#include <assert.h>

This header file defines a debugging aid.

As there is no standard error output stream available for many applications using this library, the generation of a printableerror message is not enabled by default. These messages will only be generated if the application defines the macro

__ASSERT_USE_STDERR

before including the <assert.h> header file. By default, only abort() will be called to halt the application.

23.2.2 Macro Definition Documentation

23.2.2.1 #define assert( expression )

Parameters

expression Expression to test for.

The assert() macro tests the given expression and if it is false, the calling process is terminated. A diagnostic messageis written to stderr and the function abort() is called, effectively terminating the program.

If expression is true, the assert() macro does nothing.

The assert() macro may be removed at compile time by defining NDEBUG as a macro (e.g., by using the compiler option-DNDEBUG).


114 CONTENTS

23.3 <ctype.h>: Character Operations

Character classification routines

These functions perform character classification. They return true or false status depending whether the characterpassed to the function falls into the function’s classification (i.e. isdigit() returns true if its argument is any value ’0’though ’9’, inclusive). If the input is not an unsigned char value, all of this function return false.

• int isalnum (int __c)• int isalpha (int __c)• int isascii (int __c)• int isblank (int __c)• int iscntrl (int __c)• int isdigit (int __c)• int isgraph (int __c)• int islower (int __c)• int isprint (int __c)• int ispunct (int __c)• int isspace (int __c)• int isupper (int __c)• int isxdigit (int __c)

Character convertion routines

This realization permits all possible values of integer argument. The toascii() function clears all highest bits. Thetolower() and toupper() functions return an input argument as is, if it is not an unsigned char value.

• int toascii (int __c)• int tolower (int __c)• int toupper (int __c)


These functions perform various operations on characters.

#include <ctype.h>


23.3.2.1 int isalnum ( int __c )

Checks for an alphanumeric character. It is equivalent to (isalpha(c) || isdigit(c)).

23.3.2.2 int isalpha ( int __c )

Checks for an alphabetic character. It is equivalent to (isupper(c) || islower(c)).

23.3.2.3 int isascii ( int __c )

Checks whether c is a 7-bit unsigned char value that fits into the ASCII character set.


23.3 <ctype.h>: Character Operations 115

23.3.2.4 int isblank ( int __c )

Checks for a blank character, that is, a space or a tab.

23.3.2.5 int iscntrl ( int __c )

Checks for a control character.

23.3.2.6 int isdigit ( int __c )

Checks for a digit (0 through 9).

23.3.2.7 int isgraph ( int __c )

Checks for any printable character except space.

23.3.2.8 int islower ( int __c )

Checks for a lower-case character.

23.3.2.9 int isprint ( int __c )

Checks for any printable character including space.

23.3.2.10 int ispunct ( int __c )

Checks for any printable character which is not a space or an alphanumeric character.

23.3.2.11 int isspace ( int __c )

Checks for white-space characters. For the avr-libc library, these are: space, form-feed (’\f’), newline (’\n’), carriagereturn (’\r’), horizontal tab (’\t’), and vertical tab (’\v’).

23.3.2.12 int isupper ( int __c )

Checks for an uppercase letter.

23.3.2.13 int isxdigit ( int __c )

Checks for a hexadecimal digits, i.e. one of 0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F.

23.3.2.14 int toascii ( int __c )

Converts c to a 7-bit unsigned char value that fits into the ASCII character set, by clearing the high-order bits.

Warning

Many people will be unhappy if you use this function. This function will convert accented letters into randomcharacters.

23.3.2.15 int tolower ( int __c )

Converts the letter c to lower case, if possible.

23.3.2.16 int toupper ( int __c )

Converts the letter c to upper case, if possible.


116 CONTENTS

23.4 <errno.h>: System Errors

Macros

• #define EDOM 33• #define ERANGE 34


#include <errno.h>

Some functions in the library set the global variable errno when an error occurs. The file, <errno.h>, providessymbolic names for various error codes.

Warning

The errno global variable is not safe to use in a threaded or multi-task system. A race condition can occur ifa task is interrupted between the call which sets error and when the task examines errno. If another taskchanges errno during this time, the result will be incorrect for the interrupted task.


23.4.2.1 #define EDOM 33

Domain error.

23.4.2.2 #define ERANGE 34

Range error.


23.5 <inttypes.h>: Integer Type conversions 117

23.5 <inttypes.h>: Integer Type conversions

Far pointers for memory access >64K

• typedef int32_t int_farptr_t• typedef uint32_t uint_farptr_t

macros for printf and scanf format specifiers

For C++, these are only included if __STDC_LIMIT_MACROS is defined before including <inttypes.h>.

• #define PRId8 "d"• #define PRIdLEAST8 "d"• #define PRIdFAST8 "d"• #define PRIi8 "i"• #define PRIiLEAST8 "i"• #define PRIiFAST8 "i"• #define PRId16 "d"• #define PRIdLEAST16 "d"• #define PRIdFAST16 "d"• #define PRIi16 "i"• #define PRIiLEAST16 "i"• #define PRIiFAST16 "i"• #define PRId32 "ld"• #define PRIdLEAST32 "ld"• #define PRIdFAST32 "ld"• #define PRIi32 "li"• #define PRIiLEAST32 "li"• #define PRIiFAST32 "li"• #define PRIdPTR PRId16• #define PRIiPTR PRIi16• #define PRIo8 "o"• #define PRIoLEAST8 "o"• #define PRIoFAST8 "o"• #define PRIu8 "u"• #define PRIuLEAST8 "u"• #define PRIuFAST8 "u"• #define PRIx8 "x"• #define PRIxLEAST8 "x"• #define PRIxFAST8 "x"• #define PRIX8 "X"• #define PRIXLEAST8 "X"• #define PRIXFAST8 "X"• #define PRIo16 "o"• #define PRIoLEAST16 "o"• #define PRIoFAST16 "o"• #define PRIu16 "u"• #define PRIuLEAST16 "u"• #define PRIuFAST16 "u"• #define PRIx16 "x"


118 CONTENTS

• #define PRIxLEAST16 "x"• #define PRIxFAST16 "x"• #define PRIX16 "X"• #define PRIXLEAST16 "X"• #define PRIXFAST16 "X"• #define PRIo32 "lo"• #define PRIoLEAST32 "lo"• #define PRIoFAST32 "lo"• #define PRIu32 "lu"• #define PRIuLEAST32 "lu"• #define PRIuFAST32 "lu"• #define PRIx32 "lx"• #define PRIxLEAST32 "lx"• #define PRIxFAST32 "lx"• #define PRIX32 "lX"• #define PRIXLEAST32 "lX"• #define PRIXFAST32 "lX"• #define PRIoPTR PRIo16• #define PRIuPTR PRIu16• #define PRIxPTR PRIx16• #define PRIXPTR PRIX16• #define SCNd8 "hhd"• #define SCNdLEAST8 "hhd"• #define SCNdFAST8 "hhd"• #define SCNi8 "hhi"• #define SCNiLEAST8 "hhi"• #define SCNiFAST8 "hhi"• #define SCNd16 "d"• #define SCNdLEAST16 "d"• #define SCNdFAST16 "d"• #define SCNi16 "i"• #define SCNiLEAST16 "i"• #define SCNiFAST16 "i"• #define SCNd32 "ld"• #define SCNdLEAST32 "ld"• #define SCNdFAST32 "ld"• #define SCNi32 "li"• #define SCNiLEAST32 "li"• #define SCNiFAST32 "li"• #define SCNdPTR SCNd16• #define SCNiPTR SCNi16• #define SCNo8 "hho"• #define SCNoLEAST8 "hho"• #define SCNoFAST8 "hho"• #define SCNu8 "hhu"• #define SCNuLEAST8 "hhu"• #define SCNuFAST8 "hhu"• #define SCNx8 "hhx"• #define SCNxLEAST8 "hhx"• #define SCNxFAST8 "hhx"• #define SCNo16 "o"



• #define SCNoLEAST16 "o"• #define SCNoFAST16 "o"• #define SCNu16 "u"• #define SCNuLEAST16 "u"• #define SCNuFAST16 "u"• #define SCNx16 "x"• #define SCNxLEAST16 "x"• #define SCNxFAST16 "x"• #define SCNo32 "lo"• #define SCNoLEAST32 "lo"• #define SCNoFAST32 "lo"• #define SCNu32 "lu"• #define SCNuLEAST32 "lu"• #define SCNuFAST32 "lu"• #define SCNx32 "lx"• #define SCNxLEAST32 "lx"• #define SCNxFAST32 "lx"• #define SCNoPTR SCNo16• #define SCNuPTR SCNu16• #define SCNxPTR SCNx16


#include <inttypes.h>

This header file includes the exact-width integer definitions from <stdint.h>, and extends them with additionalfacilities provided by the implementation.

Currently, the extensions include two additional integer types that could hold a "far" pointer (i.e. a code pointer that canaddress more than 64 KB), as well as standard names for all printf and scanf formatting options that are supported bythe <stdio.h>: Standard IO facilities. As the library does not support the full range of conversion specifiers from ISO9899:1999, only those conversions that are actually implemented will be listed here.

The idea behind these conversion macros is that, for each of the types defined by <stdint.h>, a macro will be suppliedthat portably allows formatting an object of that type in printf() or scanf() operations. Example:

#include <inttypes.h>

uint8_t smallval;int32_t longval;...printf("The hexadecimal value of smallval is %" PRIx8

", the decimal value of longval is %" PRId32 ".\n",smallval, longval);


23.5.2.1 #define PRId16 "d"

decimal printf format for int16_t

23.5.2.2 #define PRId32 "ld"



120 CONTENTS

23.5.2.3 #define PRId8 "d"


23.5.2.4 #define PRIdFAST16 "d"

decimal printf format for int_fast16_t

23.5.2.5 #define PRIdFAST32 "ld"


23.5.2.6 #define PRIdFAST8 "d"


23.5.2.7 #define PRIdLEAST16 "d"

decimal printf format for int_least16_t

23.5.2.8 #define PRIdLEAST32 "ld"


23.5.2.9 #define PRIdLEAST8 "d"


23.5.2.10 #define PRIdPTR PRId16

decimal printf format for intptr_t

23.5.2.11 #define PRIi16 "i"

integer printf format for int16_t

23.5.2.12 #define PRIi32 "li"


23.5.2.13 #define PRIi8 "i"


23.5.2.14 #define PRIiFAST16 "i"

integer printf format for int_fast16_t

23.5.2.15 #define PRIiFAST32 "li"


23.5.2.16 #define PRIiFAST8 "i"




23.5.2.17 #define PRIiLEAST16 "i"

integer printf format for int_least16_t

23.5.2.18 #define PRIiLEAST32 "li"


23.5.2.19 #define PRIiLEAST8 "i"


23.5.2.20 #define PRIiPTR PRIi16

integer printf format for intptr_t

23.5.2.21 #define PRIo16 "o"

octal printf format for uint16_t

23.5.2.22 #define PRIo32 "lo"


23.5.2.23 #define PRIo8 "o"


23.5.2.24 #define PRIoFAST16 "o"

octal printf format for uint_fast16_t

23.5.2.25 #define PRIoFAST32 "lo"


23.5.2.26 #define PRIoFAST8 "o"


23.5.2.27 #define PRIoLEAST16 "o"

octal printf format for uint_least16_t

23.5.2.28 #define PRIoLEAST32 "lo"


23.5.2.29 #define PRIoLEAST8 "o"


23.5.2.30 #define PRIoPTR PRIo16

octal printf format for uintptr_t


122 CONTENTS

23.5.2.31 #define PRIu16 "u"

decimal printf format for uint16_t

23.5.2.32 #define PRIu32 "lu"


23.5.2.33 #define PRIu8 "u"


23.5.2.34 #define PRIuFAST16 "u"

decimal printf format for uint_fast16_t

23.5.2.35 #define PRIuFAST32 "lu"


23.5.2.36 #define PRIuFAST8 "u"


23.5.2.37 #define PRIuLEAST16 "u"

decimal printf format for uint_least16_t

23.5.2.38 #define PRIuLEAST32 "lu"


23.5.2.39 #define PRIuLEAST8 "u"


23.5.2.40 #define PRIuPTR PRIu16

decimal printf format for uintptr_t

23.5.2.41 #define PRIx16 "x"

hexadecimal printf format for uint16_t

23.5.2.42 #define PRIX16 "X"

uppercase hexadecimal printf format for uint16_t

23.5.2.43 #define PRIx32 "lx"


23.5.2.44 #define PRIX32 "lX"




23.5.2.45 #define PRIx8 "x"


23.5.2.46 #define PRIX8 "X"


23.5.2.47 #define PRIxFAST16 "x"

hexadecimal printf format for uint_fast16_t

23.5.2.48 #define PRIXFAST16 "X"

uppercase hexadecimal printf format for uint_fast16_t

23.5.2.49 #define PRIxFAST32 "lx"


23.5.2.50 #define PRIXFAST32 "lX"


23.5.2.51 #define PRIxFAST8 "x"


23.5.2.52 #define PRIXFAST8 "X"


23.5.2.53 #define PRIxLEAST16 "x"

hexadecimal printf format for uint_least16_t

23.5.2.54 #define PRIXLEAST16 "X"

uppercase hexadecimal printf format for uint_least16_t

23.5.2.55 #define PRIxLEAST32 "lx"


23.5.2.56 #define PRIXLEAST32 "lX"


23.5.2.57 #define PRIxLEAST8 "x"


23.5.2.58 #define PRIXLEAST8 "X"



124 CONTENTS

23.5.2.59 #define PRIxPTR PRIx16

hexadecimal printf format for uintptr_t

23.5.2.60 #define PRIXPTR PRIX16

uppercase hexadecimal printf format for uintptr_t

23.5.2.61 #define SCNd16 "d"

decimal scanf format for int16_t

23.5.2.62 #define SCNd32 "ld"


23.5.2.63 #define SCNd8 "hhd"


23.5.2.64 #define SCNdFAST16 "d"

decimal scanf format for int_fast16_t

23.5.2.65 #define SCNdFAST32 "ld"


23.5.2.66 #define SCNdFAST8 "hhd"


23.5.2.67 #define SCNdLEAST16 "d"

decimal scanf format for int_least16_t

23.5.2.68 #define SCNdLEAST32 "ld"


23.5.2.69 #define SCNdLEAST8 "hhd"


23.5.2.70 #define SCNdPTR SCNd16

decimal scanf format for intptr_t

23.5.2.71 #define SCNi16 "i"

generic-integer scanf format for int16_t

23.5.2.72 #define SCNi32 "li"




23.5.2.73 #define SCNi8 "hhi"


23.5.2.74 #define SCNiFAST16 "i"

generic-integer scanf format for int_fast16_t

23.5.2.75 #define SCNiFAST32 "li"


23.5.2.76 #define SCNiFAST8 "hhi"


23.5.2.77 #define SCNiLEAST16 "i"

generic-integer scanf format for int_least16_t

23.5.2.78 #define SCNiLEAST32 "li"


23.5.2.79 #define SCNiLEAST8 "hhi"


23.5.2.80 #define SCNiPTR SCNi16

generic-integer scanf format for intptr_t

23.5.2.81 #define SCNo16 "o"

octal scanf format for uint16_t

23.5.2.82 #define SCNo32 "lo"


23.5.2.83 #define SCNo8 "hho"


23.5.2.84 #define SCNoFAST16 "o"

octal scanf format for uint_fast16_t

23.5.2.85 #define SCNoFAST32 "lo"


23.5.2.86 #define SCNoFAST8 "hho"



126 CONTENTS

23.5.2.87 #define SCNoLEAST16 "o"

octal scanf format for uint_least16_t

23.5.2.88 #define SCNoLEAST32 "lo"


23.5.2.89 #define SCNoLEAST8 "hho"


23.5.2.90 #define SCNoPTR SCNo16

octal scanf format for uintptr_t

23.5.2.91 #define SCNu16 "u"

decimal scanf format for uint16_t

23.5.2.92 #define SCNu32 "lu"


23.5.2.93 #define SCNu8 "hhu"


23.5.2.94 #define SCNuFAST16 "u"

decimal scanf format for uint_fast16_t

23.5.2.95 #define SCNuFAST32 "lu"


23.5.2.96 #define SCNuFAST8 "hhu"


23.5.2.97 #define SCNuLEAST16 "u"

decimal scanf format for uint_least16_t

23.5.2.98 #define SCNuLEAST32 "lu"


23.5.2.99 #define SCNuLEAST8 "hhu"


23.5.2.100 #define SCNuPTR SCNu16

decimal scanf format for uintptr_t



23.5.2.101 #define SCNx16 "x"

hexadecimal scanf format for uint16_t

23.5.2.102 #define SCNx32 "lx"


23.5.2.103 #define SCNx8 "hhx"


23.5.2.104 #define SCNxFAST16 "x"

hexadecimal scanf format for uint_fast16_t

23.5.2.105 #define SCNxFAST32 "lx"


23.5.2.106 #define SCNxFAST8 "hhx"


23.5.2.107 #define SCNxLEAST16 "x"

hexadecimal scanf format for uint_least16_t

23.5.2.108 #define SCNxLEAST32 "lx"


23.5.2.109 #define SCNxLEAST8 "hhx"


23.5.2.110 #define SCNxPTR SCNx16

hexadecimal scanf format for uintptr_t

23.5.3 Typedef Documentation

23.5.3.1 typedef int32_t int_farptr_t

signed integer type that can hold a pointer > 64 KB

23.5.3.2 typedef uint32_t uint_farptr_t

unsigned integer type that can hold a pointer > 64 KB


128 CONTENTS

23.6 <math.h>: Mathematics

Macros

• #define M_E 2.7182818284590452354• #define M_LOG2E 1.4426950408889634074 /∗ log_2 e ∗/• #define M_LOG10E 0.43429448190325182765 /∗ log_10 e ∗/• #define M_LN2 0.69314718055994530942 /∗ log_e 2 ∗/• #define M_LN10 2.30258509299404568402 /∗ log_e 10 ∗/• #define M_PI 3.14159265358979323846 /∗ pi ∗/• #define M_PI_2 1.57079632679489661923 /∗ pi/2 ∗/• #define M_PI_4 0.78539816339744830962 /∗ pi/4 ∗/• #define M_1_PI 0.31830988618379067154 /∗ 1/pi ∗/• #define M_2_PI 0.63661977236758134308 /∗ 2/pi ∗/• #define M_2_SQRTPI 1.12837916709551257390 /∗ 2/sqrt(pi) ∗/• #define M_SQRT2 1.41421356237309504880 /∗ sqrt(2) ∗/• #define M_SQRT1_2 0.70710678118654752440 /∗ 1/sqrt(2) ∗/• #define NAN __builtin_nan("")• #define INFINITY __builtin_inf()• #define cosf cos• #define sinf sin• #define tanf tan• #define fabsf fabs• #define fmodf fmod• #define cbrtf cbrt• #define hypotf hypot• #define squaref square• #define floorf floor• #define ceilf ceil• #define frexpf frexp• #define ldexpf ldexp• #define expf exp• #define coshf cosh• #define sinhf sinh• #define tanhf tanh• #define acosf acos• #define asinf asin• #define atanf atan• #define atan2f atan2• #define logf log• #define log10f log10• #define powf pow• #define isnanf isnan• #define isinff isinf• #define isfinitef isfinite• #define copysignf copysign• #define signbitf signbit• #define fdimf fdim• #define fmaf fma• #define fmaxf fmax• #define fminf fmin


23.6 <math.h>: Mathematics 129

• #define truncf trunc• #define roundf round• #define lroundf lround• #define lrintf lrint

Functions

• double cos (double __x)• double sin (double __x)• double tan (double __x)• double fabs (double __x)• double fmod (double __x, double __y)• double modf (double __x, double ∗__iptr)• float modff (float __x, float ∗__iptr)• double sqrt (double __x)• float sqrtf (float)• double cbrt (double __x)• double hypot (double __x, double __y)• double square (double __x)• double floor (double __x)• double ceil (double __x)• double frexp (double __x, int ∗__pexp)• double ldexp (double __x, int __exp)• double exp (double __x)• double cosh (double __x)• double sinh (double __x)• double tanh (double __x)• double acos (double __x)• double asin (double __x)• double atan (double __x)• double atan2 (double __y, double __x)• double log (double __x)• double log10 (double __x)• double pow (double __x, double __y)• int isnan (double __x)• int isinf (double __x)• static int isfinite (double __x)• static double copysign (double __x, double __y)• int signbit (double __x)• double fdim (double __x, double __y)• double fma (double __x, double __y, double __z)• double fmax (double __x, double __y)• double fmin (double __x, double __y)• double trunc (double __x)• double round (double __x)• long lround (double __x)• long lrint (double __x)


130 CONTENTS


#include <math.h>

This header file declares basic mathematics constants and functions.

Notes:

• In order to access the functions declared herein, it is usually also required to additionally link against the librarylibm.a. See also the related FAQ entry.

• Math functions do not raise exceptions and do not change the errno variable. Therefore the majority of themare declared with const attribute, for better optimization by GCC.


23.6.2.1 #define acosf acos

The alias for acos().

23.6.2.2 #define asinf asin

The alias for asin().

23.6.2.3 #define atan2f atan2

The alias for atan2().

23.6.2.4 #define atanf atan

The alias for atan().

23.6.2.5 #define cbrtf cbrt

The alias for cbrt().

23.6.2.6 #define ceilf ceil

The alias for ceil().

23.6.2.7 #define copysignf copysign

The alias for copysign().

23.6.2.8 #define cosf cos

The alias for cos().

23.6.2.9 #define coshf cosh

The alias for cosh().

23.6.2.10 #define expf exp

The alias for exp().



23.6.2.11 #define fabsf fabs

The alias for fabs().

23.6.2.12 #define fdimf fdim

The alias for fdim().

23.6.2.13 #define floorf floor

The alias for floor().

23.6.2.14 #define fmaf fma

The alias for fma().

23.6.2.15 #define fmaxf fmax

The alias for fmax().

23.6.2.16 #define fminf fmin

The alias for fmin().

23.6.2.17 #define fmodf fmod

The alias for fmod().

23.6.2.18 #define frexpf frexp

The alias for frexp().

23.6.2.19 #define hypotf hypot

The alias for hypot().

23.6.2.20 #define INFINITY __builtin_inf()

INFINITY constant.

23.6.2.21 #define isfinitef isfinite

The alias for isfinite().

23.6.2.22 #define isinff isinf

The alias for isinf().

23.6.2.23 #define isnanf isnan

The alias for isnan().

23.6.2.24 #define ldexpf ldexp

The alias for ldexp().


132 CONTENTS

23.6.2.25 #define log10f log10

The alias for log10().

23.6.2.26 #define logf log

The alias for log().

23.6.2.27 #define lrintf lrint

The alias for lrint().

23.6.2.28 #define lroundf lround

The alias for lround().

23.6.2.29 #define M_1_PI 0.31830988618379067154 /∗ 1/pi ∗/

The constant 1/pi.

23.6.2.30 #define M_2_PI 0.63661977236758134308 /∗ 2/pi ∗/

The constant 2/pi.

23.6.2.31 #define M_2_SQRTPI 1.12837916709551257390 /∗ 2/sqrt(pi) ∗/

The constant 2/sqrt(pi).

23.6.2.32 #define M_E 2.7182818284590452354

The constant e.

23.6.2.33 #define M_LN10 2.30258509299404568402 /∗ log_e 10 ∗/

The natural logarithm of the 10.

23.6.2.34 #define M_LN2 0.69314718055994530942 /∗ log_e 2 ∗/

The natural logarithm of the 2.

23.6.2.35 #define M_LOG10E 0.43429448190325182765 /∗ log_10 e ∗/

The logarithm of the e to base 10.

23.6.2.36 #define M_LOG2E 1.4426950408889634074 /∗ log_2 e ∗/

The logarithm of the e to base 2.

23.6.2.37 #define M_PI 3.14159265358979323846 /∗ pi ∗/

The constant pi.

23.6.2.38 #define M_PI_2 1.57079632679489661923 /∗ pi/2 ∗/

The constant pi/2.



23.6.2.39 #define M_PI_4 0.78539816339744830962 /∗ pi/4 ∗/

The constant pi/4.

23.6.2.40 #define M_SQRT1_2 0.70710678118654752440 /∗ 1/sqrt(2) ∗/

The constant 1/sqrt(2).

23.6.2.41 #define M_SQRT2 1.41421356237309504880 /∗ sqrt(2) ∗/

The square root of 2.

23.6.2.42 #define NAN __builtin_nan("")

NAN constant.

23.6.2.43 #define powf pow

The alias for pow().

23.6.2.44 #define roundf round

The alias for round().

23.6.2.45 #define signbitf signbit

The alias for signbit().

23.6.2.46 #define sinf sin

The alias for sin().

23.6.2.47 #define sinhf sinh

The alias for sinh().

23.6.2.48 #define squaref square

The alias for square().

23.6.2.49 #define tanf tan

The alias for tan().

23.6.2.50 #define tanhf tanh

The alias for tanh().

23.6.2.51 #define truncf trunc

The alias for trunc().



134 CONTENTS

23.6.3.1 double acos ( double __x )

The acos() function computes the principal value of the arc cosine of __x. The returned value is in the range [0, pi]radians. A domain error occurs for arguments not in the range [-1, +1].

23.6.3.2 double asin ( double __x )

The asin() function computes the principal value of the arc sine of __x. The returned value is in the range [-pi/2, pi/2]radians. A domain error occurs for arguments not in the range [-1, +1].

23.6.3.3 double atan ( double __x )

The atan() function computes the principal value of the arc tangent of __x. The returned value is in the range [-pi/2, pi/2]radians.

23.6.3.4 double atan2 ( double __y, double __x )

The atan2() function computes the principal value of the arc tangent of __y / __x, using the signs of both arguments todetermine the quadrant of the return value. The returned value is in the range [-pi, +pi] radians.

23.6.3.5 double cbrt ( double __x )

The cbrt() function returns the cube root of __x.

23.6.3.6 double ceil ( double __x )

The ceil() function returns the smallest integral value greater than or equal to __x, expressed as a floating-point number.

23.6.3.7 static double copysign ( double __x, double __y ) [static]

The copysign() function returns __x but with the sign of __y. They work even if __x or __y are NaN or zero.

23.6.3.8 double cos ( double __x )

The cos() function returns the cosine of __x, measured in radians.

23.6.3.9 double cosh ( double __x )

The cosh() function returns the hyperbolic cosine of __x.

23.6.3.10 double exp ( double __x )

The exp() function returns the exponential value of __x.

23.6.3.11 double fabs ( double __x )

The fabs() function computes the absolute value of a floating-point number __x.

23.6.3.12 double fdim ( double __x, double __y )

The fdim() function returns max(__x - __y, 0). If __x or __y or both are NaN, NaN is returned.

23.6.3.13 double floor ( double __x )

The floor() function returns the largest integral value less than or equal to __x, expressed as a floating-point number.



23.6.3.14 double fma ( double __x, double __y, double __z )

The fma() function performs floating-point multiply-add. This is the operation (__x ∗ __y) + __z, but the intermediateresult is not rounded to the destination type. This can sometimes improve the precision of a calculation.

23.6.3.15 double fmax ( double __x, double __y )

The fmax() function returns the greater of the two values __x and __y. If an argument is NaN, the other argument isreturned. If both arguments are NaN, NaN is returned.

23.6.3.16 double fmin ( double __x, double __y )

The fmin() function returns the lesser of the two values __x and __y. If an argument is NaN, the other argument isreturned. If both arguments are NaN, NaN is returned.

23.6.3.17 double fmod ( double __x, double __y )

The function fmod() returns the floating-point remainder of __x / __y.

23.6.3.18 double frexp ( double __x, int ∗ __pexp )

The frexp() function breaks a floating-point number into a normalized fraction and an integral power of 2. It stores theinteger in the int object pointed to by __pexp.

If __x is a normal float point number, the frexp() function returns the value v, such that v has a magnitude in the interval[1/2, 1) or zero, and __x equals v times 2 raised to the power __pexp. If __x is zero, both parts of the result are zero. If__x is not a finite number, the frexp() returns __x as is and stores 0 by __pexp.

Note

This implementation permits a zero pointer as a directive to skip a storing the exponent.

23.6.3.19 double hypot ( double __x, double __y )

The hypot() function returns sqrt(__x∗__x + __y∗__y). This is the length of the hypotenuse of a right triangle with sidesof length __x and __y, or the distance of the point (__x, __y) from the origin. Using this function instead of the directformula is wise, since the error is much smaller. No underflow with small __x and __y. No overflow if result is in range.

23.6.3.20 static int isfinite ( double __x ) [static]

The isfinite() function returns a nonzero value if __x is finite: not plus or minus infinity, and not NaN.

23.6.3.21 int isinf ( double __x )

The function isinf() returns 1 if the argument __x is positive infinity, -1 if __x is negative infinity, and 0 otherwise.

Note

The GCC 4.3 can replace this function with inline code that returns the 1 value for both infinities (gcc bug #35509).

23.6.3.22 int isnan ( double __x )

The function isnan() returns 1 if the argument __x represents a "not-a-number" (NaN) object, otherwise 0.

23.6.3.23 double ldexp ( double __x, int __exp )

The ldexp() function multiplies a floating-point number by an integral power of 2. It returns the value of __x times 2raised to the power __exp.


136 CONTENTS

23.6.3.24 double log ( double __x )

The log() function returns the natural logarithm of argument __x.

23.6.3.25 double log10 ( double __x )

The log10() function returns the logarithm of argument __x to base 10.

23.6.3.26 long lrint ( double __x )

The lrint() function rounds __x to the nearest integer, rounding the halfway cases to the even integer direction. (That isboth 1.5 and 2.5 values are rounded to 2). This function is similar to rint() function, but it differs in type of return valueand in that an overflow is possible.

Returns

The rounded long integer value. If __x is not a finite number or an overflow was, this realization returns theLONG_MIN value (0x80000000).

23.6.3.27 long lround ( double __x )

The lround() function rounds __x to the nearest integer, but rounds halfway cases away from zero (instead of to thenearest even integer). This function is similar to round() function, but it differs in type of return value and in that anoverflow is possible.

Returns

The rounded long integer value. If __x is not a finite number or an overflow was, this realization returns theLONG_MIN value (0x80000000).

23.6.3.28 double modf ( double __x, double ∗ __iptr )

The modf() function breaks the argument __x into integral and fractional parts, each of which has the same sign as theargument. It stores the integral part as a double in the object pointed to by __iptr.

The modf() function returns the signed fractional part of __x.

Note

This implementation skips writing by zero pointer. However, the GCC 4.3 can replace this function with inline codethat does not permit to use NULL address for the avoiding of storing.

23.6.3.29 float modff ( float __x, float ∗ __iptr )

The alias for modf().

23.6.3.30 double pow ( double __x, double __y )

The function pow() returns the value of __x to the exponent __y.

23.6.3.31 double round ( double __x )

The round() function rounds __x to the nearest integer, but rounds halfway cases away from zero (instead of to thenearest even integer). Overflow is impossible.

Returns

The rounded value. If __x is an integral or infinite, __x itself is returned. If __x is NaN, then NaN is returned.



23.6.3.32 int signbit ( double __x )

The signbit() function returns a nonzero value if the value of __x has its sign bit set. This is not the same as ‘__x < 0.0’,because IEEE 754 floating point allows zero to be signed. The comparison ‘-0.0 < 0.0’ is false, but ‘signbit (-0.0)’ willreturn a nonzero value.

23.6.3.33 double sin ( double __x )

The sin() function returns the sine of __x, measured in radians.

23.6.3.34 double sinh ( double __x )

The sinh() function returns the hyperbolic sine of __x.

23.6.3.35 double sqrt ( double __x )

The sqrt() function returns the non-negative square root of __x.

23.6.3.36 double square ( double __x )

The function square() returns __x ∗ __x.

Note

This function does not belong to the C standard definition.

23.6.3.37 double tan ( double __x )

The tan() function returns the tangent of __x, measured in radians.

23.6.3.38 double tanh ( double __x )

The tanh() function returns the hyperbolic tangent of __x.

23.6.3.39 double trunc ( double __x )

The trunc() function rounds __x to the nearest integer not larger in absolute value.


138 CONTENTS

23.7 <setjmp.h>: Non-local goto

Functions

• int setjmp (jmp_buf __jmpb)• void longjmp (jmp_buf __jmpb, int __ret) __ATTR_NORETURN__


While the C language has the dreaded goto statement, it can only be used to jump to a label in the same (local)function. In order to jump directly to another (non-local) function, the C library provides the setjmp() and longjmp()functions. setjmp() and longjmp() are useful for dealing with errors and interrupts encountered in a low-level subroutineof a program.

Note

setjmp() and longjmp() make programs hard to understand and maintain. If possible, an alternative should beused.longjmp() can destroy changes made to global register variables (see How to permanently bind a variable to aregister?).

For a very detailed discussion of setjmp()/longjmp(), see Chapter 7 of Advanced Programming in the UNIX Environment,by W. Richard Stevens.

Example:

#include <setjmp.h>

jmp_buf env;

int main (void){

if (setjmp (env)){

... handle error ...}

while (1){

... main processing loop which calls foo() some where ...}

}

...

void foo (void){

... blah, blah, blah ...

if (err){

longjmp (env, 1);}

}


23.7.2.1 void longjmp ( jmp_buf __jmpb, int __ret )

Non-local jump to a saved stack context.

#include <setjmp.h>


23.7 <setjmp.h>: Non-local goto 139

longjmp() restores the environment saved by the last call of setjmp() with the corresponding __jmpb argument. Afterlongjmp() is completed, program execution continues as if the corresponding call of setjmp() had just returned the value__ret.

Note

longjmp() cannot cause 0 to be returned. If longjmp() is invoked with a second argument of 0, 1 will be returnedinstead.

Parameters

__jmpb Information saved by a previous call to setjmp().__ret Value to return to the caller of setjmp().

Returns

This function never returns.

23.7.2.2 int setjmp ( jmp_buf __jmpb )

Save stack context for non-local goto.

#include <setjmp.h>

setjmp() saves the stack context/environment in __jmpb for later use by longjmp(). The stack context will be invalidatedif the function which called setjmp() returns.

Parameters

__jmpb Variable of type jmp_buf which holds the stack information such that the environment can berestored.

Returns

setjmp() returns 0 if returning directly, and non-zero when returning from longjmp() using the saved context.


140 CONTENTS

23.8 <stdint.h>: Standard Integer Types

Exact-width integer types

Integer types having exactly the specified width

• typedef signed char int8_t• typedef unsigned char uint8_t• typedef signed int int16_t• typedef unsigned int uint16_t• typedef signed long int int32_t• typedef unsigned long int uint32_t• typedef signed long long int int64_t• typedef unsigned long long int uint64_t

Integer types capable of holding object pointers

These allow you to declare variables of the same size as a pointer.

• typedef int16_t intptr_t• typedef uint16_t uintptr_t

Minimum-width integer types

Integer types having at least the specified width

• typedef int8_t int_least8_t• typedef uint8_t uint_least8_t• typedef int16_t int_least16_t• typedef uint16_t uint_least16_t• typedef int32_t int_least32_t• typedef uint32_t uint_least32_t• typedef int64_t int_least64_t• typedef uint64_t uint_least64_t

Fastest minimum-width integer types

Integer types being usually fastest having at least the specified width

• typedef int8_t int_fast8_t• typedef uint8_t uint_fast8_t• typedef int16_t int_fast16_t• typedef uint16_t uint_fast16_t• typedef int32_t int_fast32_t• typedef uint32_t uint_fast32_t• typedef int64_t int_fast64_t• typedef uint64_t uint_fast64_t


23.8 <stdint.h>: Standard Integer Types 141

Greatest-width integer types

Types designating integer data capable of representing any value of any integer type in the corresponding signed orunsigned category

• typedef int64_t intmax_t• typedef uint64_t uintmax_t

Limits of specified-width integer types

C++ implementations should define these macros only when __STDC_LIMIT_MACROS is defined before <stdint.h>is included

• #define INT8_MAX 0x7f• #define INT8_MIN (-INT8_MAX - 1)• #define UINT8_MAX (INT8_MAX ∗ 2 + 1)• #define INT16_MAX 0x7fff• #define INT16_MIN (-INT16_MAX - 1)• #define UINT16_MAX (__CONCAT(INT16_MAX, U) ∗ 2U + 1U)• #define INT32_MAX 0x7fffffffL• #define INT32_MIN (-INT32_MAX - 1L)• #define UINT32_MAX (__CONCAT(INT32_MAX, U) ∗ 2UL + 1UL)• #define INT64_MAX 0x7fffffffffffffffLL• #define INT64_MIN (-INT64_MAX - 1LL)• #define UINT64_MAX (__CONCAT(INT64_MAX, U) ∗ 2ULL + 1ULL)

Limits of minimum-width integer types

• #define INT_LEAST8_MAX INT8_MAX• #define INT_LEAST8_MIN INT8_MIN• #define UINT_LEAST8_MAX UINT8_MAX• #define INT_LEAST16_MAX INT16_MAX• #define INT_LEAST16_MIN INT16_MIN• #define UINT_LEAST16_MAX UINT16_MAX• #define INT_LEAST32_MAX INT32_MAX• #define INT_LEAST32_MIN INT32_MIN• #define UINT_LEAST32_MAX UINT32_MAX• #define INT_LEAST64_MAX INT64_MAX• #define INT_LEAST64_MIN INT64_MIN• #define UINT_LEAST64_MAX UINT64_MAX

Limits of fastest minimum-width integer types

• #define INT_FAST8_MAX INT8_MAX• #define INT_FAST8_MIN INT8_MIN• #define UINT_FAST8_MAX UINT8_MAX• #define INT_FAST16_MAX INT16_MAX• #define INT_FAST16_MIN INT16_MIN• #define UINT_FAST16_MAX UINT16_MAX• #define INT_FAST32_MAX INT32_MAX


142 CONTENTS

• #define INT_FAST32_MIN INT32_MIN• #define UINT_FAST32_MAX UINT32_MAX• #define INT_FAST64_MAX INT64_MAX• #define INT_FAST64_MIN INT64_MIN• #define UINT_FAST64_MAX UINT64_MAX

Limits of integer types capable of holding object pointers

• #define INTPTR_MAX INT16_MAX• #define INTPTR_MIN INT16_MIN• #define UINTPTR_MAX UINT16_MAX

Limits of greatest-width integer types

• #define INTMAX_MAX INT64_MAX• #define INTMAX_MIN INT64_MIN• #define UINTMAX_MAX UINT64_MAX

Limits of other integer types

C++ implementations should define these macros only when __STDC_LIMIT_MACROS is defined before <stdint.h>is included

• #define PTRDIFF_MAX INT16_MAX• #define PTRDIFF_MIN INT16_MIN• #define SIG_ATOMIC_MAX INT8_MAX• #define SIG_ATOMIC_MIN INT8_MIN• #define SIZE_MAX UINT16_MAX• #define WCHAR_MAX __WCHAR_MAX__• #define WCHAR_MIN __WCHAR_MIN__• #define WINT_MAX __WINT_MAX__• #define WINT_MIN __WINT_MIN__

Macros for integer constants

C++ implementations should define these macros only when __STDC_CONSTANT_MACROS is defined before<stdint.h> is included.

These definitions are valid for integer constants without suffix and for macros defined as integer constant without suffix

• #define INT8_C(value) ((int8_t) value)• #define UINT8_C(value) ((uint8_t) __CONCAT(value, U))• #define INT16_C(value) value• #define UINT16_C(value) __CONCAT(value, U)• #define INT32_C(value) __CONCAT(value, L)• #define UINT32_C(value) __CONCAT(value, UL)• #define INT64_C(value) __CONCAT(value, LL)• #define UINT64_C(value) __CONCAT(value, ULL)• #define INTMAX_C(value) __CONCAT(value, LL)• #define UINTMAX_C(value) __CONCAT(value, ULL)




#include <stdint.h>

Use [u]intN_t if you need exactly N bits.

Since these typedefs are mandated by the C99 standard, they are preferred over rolling your own typedefs.


23.8.2.1 #define INT16_C( value ) value

define a constant of type int16_t

23.8.2.2 #define INT16_MAX 0x7fff

largest positive value an int16_t can hold.

23.8.2.3 #define INT16_MIN (-INT16_MAX - 1)

smallest negative value an int16_t can hold.

23.8.2.4 #define INT32_C( value ) __CONCAT(value, L)


23.8.2.5 #define INT32_MAX 0x7fffffffL


23.8.2.6 #define INT32_MIN (-INT32_MAX - 1L)


23.8.2.7 #define INT64_C( value ) __CONCAT(value, LL)


23.8.2.8 #define INT64_MAX 0x7fffffffffffffffLL


23.8.2.9 #define INT64_MIN (-INT64_MAX - 1LL)


23.8.2.10 #define INT8_C( value ) ((int8_t) value)


23.8.2.11 #define INT8_MAX 0x7f


23.8.2.12 #define INT8_MIN (-INT8_MAX - 1)



144 CONTENTS

23.8.2.13 #define INT_FAST16_MAX INT16_MAX

largest positive value an int_fast16_t can hold.

23.8.2.14 #define INT_FAST16_MIN INT16_MIN

smallest negative value an int_fast16_t can hold.













23.8.2.21 #define INT_LEAST16_MAX INT16_MAX

largest positive value an int_least16_t can hold.

23.8.2.22 #define INT_LEAST16_MIN INT16_MIN

smallest negative value an int_least16_t can hold.















23.8.2.29 #define INTMAX_C( value ) __CONCAT(value, LL)

define a constant of type intmax_t

23.8.2.30 #define INTMAX_MAX INT64_MAX

largest positive value an intmax_t can hold.

23.8.2.31 #define INTMAX_MIN INT64_MIN

smallest negative value an intmax_t can hold.

23.8.2.32 #define INTPTR_MAX INT16_MAX

largest positive value an intptr_t can hold.

23.8.2.33 #define INTPTR_MIN INT16_MIN

smallest negative value an intptr_t can hold.

23.8.2.34 #define PTRDIFF_MAX INT16_MAX

largest positive value a ptrdiff_t can hold.

23.8.2.35 #define PTRDIFF_MIN INT16_MIN

smallest negative value a ptrdiff_t can hold.

23.8.2.36 #define SIG_ATOMIC_MAX INT8_MAX

largest positive value a sig_atomic_t can hold.

23.8.2.37 #define SIG_ATOMIC_MIN INT8_MIN

smallest negative value a sig_atomic_t can hold.

23.8.2.38 #define SIZE_MAX UINT16_MAX

largest value a size_t can hold.

23.8.2.39 #define UINT16_C( value ) __CONCAT(value, U)

define a constant of type uint16_t

23.8.2.40 #define UINT16_MAX (__CONCAT(INT16_MAX, U) ∗ 2U + 1U)

largest value an uint16_t can hold.


146 CONTENTS

23.8.2.41 #define UINT32_C( value ) __CONCAT(value, UL)


23.8.2.42 #define UINT32_MAX (__CONCAT(INT32_MAX, U) ∗ 2UL + 1UL)


23.8.2.43 #define UINT64_C( value ) __CONCAT(value, ULL)


23.8.2.44 #define UINT64_MAX (__CONCAT(INT64_MAX, U) ∗ 2ULL + 1ULL)


23.8.2.45 #define UINT8_C( value ) ((uint8_t) __CONCAT(value, U))


23.8.2.46 #define UINT8_MAX (INT8_MAX ∗ 2 + 1)


23.8.2.47 #define UINT_FAST16_MAX UINT16_MAX

largest value an uint_fast16_t can hold.







23.8.2.51 #define UINT_LEAST16_MAX UINT16_MAX

largest value an uint_least16_t can hold.









23.8.2.55 #define UINTMAX_C( value ) __CONCAT(value, ULL)

define a constant of type uintmax_t

23.8.2.56 #define UINTMAX_MAX UINT64_MAX

largest value an uintmax_t can hold.

23.8.2.57 #define UINTPTR_MAX UINT16_MAX

largest value an uintptr_t can hold.


23.8.3.1 typedef signed int int16_t

16-bit signed type.

23.8.3.2 typedef signed long int int32_t

32-bit signed type.

23.8.3.3 typedef signed long long int int64_t

64-bit signed type.

Note

This type is not available when the compiler option -mint8 is in effect.

23.8.3.4 typedef signed char int8_t

8-bit signed type.

23.8.3.5 typedef int16_t int_fast16_t

fastest signed int with at least 16 bits.





Note




23.8.3.9 typedef int16_t int_least16_t

signed int with at least 16 bits.


148 CONTENTS





Note




23.8.3.13 typedef int64_t intmax_t

largest signed int available.

23.8.3.14 typedef int16_t intptr_t

Signed pointer compatible type.

23.8.3.15 typedef unsigned int uint16_t

16-bit unsigned type.

23.8.3.16 typedef unsigned long int uint32_t


23.8.3.17 typedef unsigned long long int uint64_t


Note


23.8.3.18 typedef unsigned char uint8_t


23.8.3.19 typedef uint16_t uint_fast16_t

fastest unsigned int with at least 16 bits.







Note




23.8.3.23 typedef uint16_t uint_least16_t

unsigned int with at least 16 bits.





Note




23.8.3.27 typedef uint64_t uintmax_t

largest unsigned int available.

23.8.3.28 typedef uint16_t uintptr_t

Unsigned pointer compatible type.


150 CONTENTS

23.9 <stdio.h>: Standard IO facilities

Macros

• #define stdin (__iob[0])• #define stdout (__iob[1])• #define stderr (__iob[2])• #define EOF (-1)• #define fdev_set_udata(stream, u) do { (stream)->udata = u; } while(0)• #define fdev_get_udata(stream) ((stream)->udata)• #define fdev_setup_stream(stream, put, get, rwflag)• #define _FDEV_SETUP_READ __SRD• #define _FDEV_SETUP_WRITE __SWR• #define _FDEV_SETUP_RW (__SRD|__SWR)• #define _FDEV_ERR (-1)• #define _FDEV_EOF (-2)• #define FDEV_SETUP_STREAM(put, get, rwflag)• #define fdev_close()• #define putc(__c, __stream) fputc(__c, __stream)• #define putchar(__c) fputc(__c, stdout)• #define getc(__stream) fgetc(__stream)• #define getchar() fgetc(stdin)• #define BUFSIZ 1024• #define _IONBF 0

Typedefs

• typedef struct __file FILE• typedef long long fpos_t

Functions

• int fclose (FILE ∗__stream)• int vfprintf (FILE ∗__stream, const char ∗__fmt, va_list __ap)• int vfprintf_P (FILE ∗__stream, const char ∗__fmt, va_list __ap)• int fputc (int __c, FILE ∗__stream)• int printf (const char ∗__fmt,...)• int printf_P (const char ∗__fmt,...)• int vprintf (const char ∗__fmt, va_list __ap)• int sprintf (char ∗__s, const char ∗__fmt,...)• int sprintf_P (char ∗__s, const char ∗__fmt,...)• int snprintf (char ∗__s, size_t __n, const char ∗__fmt,...)• int snprintf_P (char ∗__s, size_t __n, const char ∗__fmt,...)• int vsprintf (char ∗__s, const char ∗__fmt, va_list ap)• int vsprintf_P (char ∗__s, const char ∗__fmt, va_list ap)• int vsnprintf (char ∗__s, size_t __n, const char ∗__fmt, va_list ap)• int vsnprintf_P (char ∗__s, size_t __n, const char ∗__fmt, va_list ap)• int fprintf (FILE ∗__stream, const char ∗__fmt,...)• int fprintf_P (FILE ∗__stream, const char ∗__fmt,...)• int fputs (const char ∗__str, FILE ∗__stream)


23.9 <stdio.h>: Standard IO facilities 151

• int fputs_P (const char ∗__str, FILE ∗__stream)

• int puts (const char ∗__str)

• int puts_P (const char ∗__str)

• size_t fwrite (const void ∗__ptr, size_t __size, size_t __nmemb, FILE ∗__stream)

• int fgetc (FILE ∗__stream)

• int ungetc (int __c, FILE ∗__stream)

• char ∗ fgets (char ∗__str, int __size, FILE ∗__stream)

• char ∗ gets (char ∗__str)

• size_t fread (void ∗__ptr, size_t __size, size_t __nmemb, FILE ∗__stream)

• void clearerr (FILE ∗__stream)

• int feof (FILE ∗__stream)

• int ferror (FILE ∗__stream)

• int vfscanf (FILE ∗__stream, const char ∗__fmt, va_list __ap)

• int vfscanf_P (FILE ∗__stream, const char ∗__fmt, va_list __ap)

• int fscanf (FILE ∗__stream, const char ∗__fmt,...)

• int fscanf_P (FILE ∗__stream, const char ∗__fmt,...)

• int scanf (const char ∗__fmt,...)

• int scanf_P (const char ∗__fmt,...)

• int vscanf (const char ∗__fmt, va_list __ap)

• int sscanf (const char ∗__buf, const char ∗__fmt,...)

• int sscanf_P (const char ∗__buf, const char ∗__fmt,...)

• int fflush (FILE ∗stream)

• int fgetpos (FILE ∗stream, fpos_t ∗pos)

• FILE ∗ fopen (const char ∗path, const char ∗mode)

• FILE ∗ freopen (const char ∗path, const char ∗mode, FILE ∗stream)

• FILE ∗ fdopen (int, const char ∗)• int fseek (FILE ∗stream, long offset, int whence)

• int fsetpos (FILE ∗stream, fpos_t ∗pos)

• long ftell (FILE ∗stream)

• int fileno (FILE ∗)• void perror (const char ∗s)

• int remove (const char ∗pathname)

• int rename (const char ∗oldpath, const char ∗newpath)

• void rewind (FILE ∗stream)

• void setbuf (FILE ∗stream, char ∗buf)

• int setvbuf (FILE ∗stream, char ∗buf, int mode, size_t size)

• FILE ∗ tmpfile (void)

• char ∗ tmpnam (char ∗s)

• FILE ∗ fdevopen (int(∗put)(char, FILE ∗), int(∗get)(FILE ∗))


#include <stdio.h>


152 CONTENTS

Introduction to the Standard IO facilities

This file declares the standard IO facilities that are implemented in avr-libc. Due to the nature of the underlyinghardware, only a limited subset of standard IO is implemented. There is no actual file implementation available, so onlydevice IO can be performed. Since there’s no operating system, the application needs to provide enough details abouttheir devices in order to make them usable by the standard IO facilities.

Due to space constraints, some functionality has not been implemented at all (like some of the printf conversions thathave been left out). Nevertheless, potential users of this implementation should be warned: the printf and scanffamilies of functions, although usually associated with presumably simple things like the famous "Hello, world!" program,are actually fairly complex which causes their inclusion to eat up a fair amount of code space. Also, they are not fast dueto the nature of interpreting the format string at run-time. Whenever possible, resorting to the (sometimes non-standard)predetermined conversion facilities that are offered by avr-libc will usually cost much less in terms of speed and codesize.

Tunable options for code size vs. feature set

In order to allow programmers a code size vs. functionality tradeoff, the function vfprintf() which is the heart of theprintf family can be selected in different flavours using linker options. See the documentation of vfprintf() for a detaileddescription. The same applies to vfscanf() and the scanf family of functions.

Outline of the chosen API

The standard streams stdin, stdout, and stderr are provided, but contrary to the C standard, since avr-libc hasno knowledge about applicable devices, these streams are not already pre-initialized at application startup. Also, sincethere is no notion of "file" whatsoever to avr-libc, there is no function fopen() that could be used to associate a streamto some device. (See note 1.) Instead, the function fdevopen() is provided to associate a stream to a device, wherethe device needs to provide a function to send a character, to receive a character, or both. There is no differentiationbetween "text" and "binary" streams inside avr-libc. Character \n is sent literally down to the device’s put() function.If the device requires a carriage return (\r) character to be sent before the linefeed, its put() routine must implementthis (see note 2).

As an alternative method to fdevopen(), the macro fdev_setup_stream() might be used to setup a user-supplied FILEstructure.

It should be noted that the automatic conversion of a newline character into a carriage return - newline sequence breaksbinary transfers. If binary transfers are desired, no automatic conversion should be performed, but instead any stringthat aims to issue a CR-LF sequence must use "\r\n" explicitly.

For convenience, the first call to fdevopen() that opens a stream for reading will cause the resulting stream to bealiased to stdin. Likewise, the first call to fdevopen() that opens a stream for writing will cause the resultingstream to be aliased to both, stdout, and stderr. Thus, if the open was done with both, read and write intent,all three standard streams will be identical. Note that these aliases are indistinguishable from each other, thus callingfclose() on such a stream will also effectively close all of its aliases (note 3).

It is possible to tie additional user data to a stream, using fdev_set_udata(). The backend put and get functions can thenextract this user data using fdev_get_udata(), and act appropriately. For example, a single put function could be used totalk to two different UARTs that way, or the put and get functions could keep internal state between calls there.

Format strings in flash ROM

All the printf and scanf family functions come in two flavours: the standard name, where the format string isexpected to be in SRAM, as well as a version with the suffix "_P" where the format string is expected to reside inthe flash ROM. The macro PSTR (explained in <avr/pgmspace.h>: Program Space Utilities) becomes very handy fordeclaring these format strings.



Running stdio without malloc()

By default, fdevopen() requires malloc(). As this is often not desired in the limited environment of a microcontroller, analternative option is provided to run completely without malloc().

The macro fdev_setup_stream() is provided to prepare a user-supplied FILE buffer for operation with stdio.

Example

#include <stdio.h>

static int uart_putchar(char c, FILE *stream);

static FILE mystdout = FDEV_SETUP_STREAM(uart_putchar, NULL,_FDEV_SETUP_WRITE);

static intuart_putchar(char c, FILE *stream){

if (c == ’\n’)uart_putchar(’\r’, stream);

loop_until_bit_is_set(UCSRA, UDRE);UDR = c;return 0;

}

intmain(void){

init_uart();stdout = &mystdout;printf("Hello, world!\n");

return 0;}

This example uses the initializer form FDEV_SETUP_STREAM() rather than the function-like fdev_setup_stream(), soall data initialization happens during C start-up.

If streams initialized that way are no longer needed, they can be destroyed by first calling the macro fdev_close(), andthen destroying the object itself. No call to fclose() should be issued for these streams. While calling fclose() itself isharmless, it will cause an undefined reference to free() and thus cause the linker to link the malloc module into theapplication.

Notes

Note 1:

It might have been possible to implement a device abstraction that is compatible with fopen() but since this wouldhave required to parse a string, and to take all the information needed either out of this string, or out of an additionaltable that would need to be provided by the application, this approach was not taken.

Note 2:

This basically follows the Unix approach: if a device such as a terminal needs special handling, it is in the domain ofthe terminal device driver to provide this functionality. Thus, a simple function suitable as put() for fdevopen()that talks to a UART interface might look like this:

intuart_putchar(char c, FILE *stream){

if (c == ’\n’)uart_putchar(’\r’);

loop_until_bit_is_set(UCSRA, UDRE);UDR = c;return 0;

}


154 CONTENTS

Note 3:

This implementation has been chosen because the cost of maintaining an alias is considerably smaller than thecost of maintaining full copies of each stream. Yet, providing an implementation that offers the complete set ofstandard streams was deemed to be useful. Not only that writing printf() instead of fprintf(mystream,...) saves typing work, but since avr-gcc needs to resort to pass all arguments of variadic functions on the stack(as opposed to passing them in registers for functions that take a fixed number of parameters), the ability to passone parameter less by implying stdin or stdout will also save some execution time.


23.9.2.1 #define _FDEV_EOF (-2)

Return code for an end-of-file condition during device read.

To be used in the get function of fdevopen().

23.9.2.2 #define _FDEV_ERR (-1)

Return code for an error condition during device read.

To be used in the get function of fdevopen().

23.9.2.3 #define _FDEV_SETUP_READ __SRD

fdev_setup_stream() with read intent

23.9.2.4 #define _FDEV_SETUP_RW (__SRD|__SWR)

fdev_setup_stream() with read/write intent

23.9.2.5 #define _FDEV_SETUP_WRITE __SWR

fdev_setup_stream() with write intent

23.9.2.6 #define EOF (-1)

EOF declares the value that is returned by various standard IO functions in case of an error. Since the AVR platform(currently) doesn’t contain an abstraction for actual files, its origin as "end of file" is somewhat meaningless here.

23.9.2.7 #define fdev_close( )

This macro frees up any library resources that might be associated with stream. It should be called if stream is nolonger needed, right before the application is going to destroy the stream object itself.

(Currently, this macro evaluates to nothing, but this might change in future versions of the library.)

23.9.2.8 #define fdev_get_udata( stream ) ((stream)->udata)

This macro retrieves a pointer to user defined data from a FILE stream object.

23.9.2.9 #define fdev_set_udata( stream, u ) do { (stream)->udata = u; } while(0)

This macro inserts a pointer to user defined data into a FILE stream object.

The user data can be useful for tracking state in the put and get functions supplied to the fdevopen() function.



23.9.2.10 #define fdev_setup_stream( stream, put, get, rwflag )

Setup a user-supplied buffer as an stdio stream.

This macro takes a user-supplied buffer stream, and sets it up as a stream that is valid for stdio operations, similar toone that has been obtained dynamically from fdevopen(). The buffer to setup must be of type FILE.

The arguments put and get are identical to those that need to be passed to fdevopen().

The rwflag argument can take one of the values _FDEV_SETUP_READ, _FDEV_SETUP_WRITE, or _FDEV_SE←↩TUP_RW, for read, write, or read/write intent, respectively.

Note

No assignments to the standard streams will be performed by fdev_setup_stream(). If standard streams are to beused, these need to be assigned by the user. See also under Running stdio without malloc().

23.9.2.11 #define FDEV_SETUP_STREAM( put, get, rwflag )

Initializer for a user-supplied stdio stream.

This macro acts similar to fdev_setup_stream(), but it is to be used as the initializer of a variable of type FILE.

The remaining arguments are to be used as explained in fdev_setup_stream().

23.9.2.12 #define getc( __stream ) fgetc(__stream)

The macro getc used to be a "fast" macro implementation with a functionality identical to fgetc(). For space constraints,in avr-libc, it is just an alias for fgetc.

23.9.2.13 #define getchar( void ) fgetc(stdin)

The macro getchar reads a character from stdin. Return values and error handling is identical to fgetc().

23.9.2.14 #define putc( __c, __stream ) fputc(__c, __stream)

The macro putc used to be a "fast" macro implementation with a functionality identical to fputc(). For space constraints,in avr-libc, it is just an alias for fputc.

23.9.2.15 #define putchar( __c ) fputc(__c, stdout)

The macro putchar sends character c to stdout.

23.9.2.16 #define stderr (__iob[2])

Stream destined for error output. Unless specifically assigned, identical to stdout.

If stderr should point to another stream, the result of another fdevopen() must be explicitly assigned to it withoutclosing the previous stderr (since this would also close stdout).

23.9.2.17 #define stdin (__iob[0])

Stream that will be used as an input stream by the simplified functions that don’t take a stream argument.

The first stream opened with read intent using fdevopen() will be assigned to stdin.

23.9.2.18 #define stdout (__iob[1])

Stream that will be used as an output stream by the simplified functions that don’t take a stream argument.

The first stream opened with write intent using fdevopen() will be assigned to both, stdin, and stderr.


156 CONTENTS


23.9.3.1 typedef struct __file FILE

FILE is the opaque structure that is passed around between the various standard IO functions.


23.9.4.1 void clearerr ( FILE ∗ __stream )

Clear the error and end-of-file flags of stream.

23.9.4.2 int fclose ( FILE ∗ __stream )

This function closes stream, and disallows and further IO to and from it.

When using fdevopen() to setup the stream, a call to fclose() is needed in order to free the internal resources allocated.

If the stream has been set up using fdev_setup_stream() or FDEV_SETUP_STREAM(), use fdev_close() instead.

It currently always returns 0 (for success).

23.9.4.3 FILE∗ fdevopen ( int(∗)(char, FILE ∗) put, int(∗)(FILE ∗) get )

This function is a replacement for fopen().

It opens a stream for a device where the actual device implementation needs to be provided by the application. Ifsuccessful, a pointer to the structure for the opened stream is returned. Reasons for a possible failure currently includethat neither the put nor the get argument have been provided, thus attempting to open a stream with no IO intent atall, or that insufficient dynamic memory is available to establish a new stream.

If the put function pointer is provided, the stream is opened with write intent. The function passed as put shall taketwo arguments, the first a character to write to the device, and the second a pointer to FILE, and shall return 0 if theoutput was successful, and a nonzero value if the character could not be sent to the device.

If the get function pointer is provided, the stream is opened with read intent. The function passed as get shall takea pointer to FILE as its single argument, and return one character from the device, passed as an int type. If an erroroccurs when trying to read from the device, it shall return _FDEV_ERR. If an end-of-file condition was reached whilereading from the device, _FDEV_EOF shall be returned.

If both functions are provided, the stream is opened with read and write intent.

The first stream opened with read intent is assigned to stdin, and the first one opened with write intent is assigned toboth, stdout and stderr.

fdevopen() uses calloc() (und thus malloc()) in order to allocate the storage for the new stream.

Note

If the macro __STDIO_FDEVOPEN_COMPAT_12 is declared before including <stdio.h>, a function prototype forfdevopen() will be chosen that is backwards compatible with avr-libc version 1.2 and before. This is solely intentedfor providing a simple migration path without the need to immediately change all source code. Do not use for newcode.

23.9.4.4 int feof ( FILE ∗ __stream )

Test the end-of-file flag of stream. This flag can only be cleared by a call to clearerr().



23.9.4.5 int ferror ( FILE ∗ __stream )

Test the error flag of stream. This flag can only be cleared by a call to clearerr().

23.9.4.6 int fflush ( FILE ∗ stream )

Flush stream.

This is a null operation provided for source-code compatibility only, as the standard IO implementation currently doesnot perform any buffering.

23.9.4.7 int fgetc ( FILE ∗ __stream )

The function fgetc reads a character from stream. It returns the character, or EOF in case end-of-file was en-countered or an error occurred. The routines feof() or ferror() must be used to distinguish between both situations.

23.9.4.8 char∗ fgets ( char ∗ __str, int __size, FILE ∗ __stream )

Read at most size - 1 bytes from stream, until a newline character was encountered, and store the characters inthe buffer pointed to by str. Unless an error was encountered while reading, the string will then be terminated with aNUL character.

If an error was encountered, the function returns NULL and sets the error flag of stream, which can be tested usingferror(). Otherwise, a pointer to the string will be returned.

23.9.4.9 int fprintf ( FILE ∗ __stream, const char ∗ __fmt, ... )

The function fprintf performs formatted output to stream. See vfprintf() for details.

23.9.4.10 int fprintf_P ( FILE ∗ __stream, const char ∗ __fmt, ... )

Variant of fprintf() that uses a fmt string that resides in program memory.

23.9.4.11 int fputc ( int __c, FILE ∗ __stream )

The function fputc sends the character c (though given as type int) to stream. It returns the character, or EOF incase an error occurred.

23.9.4.12 int fputs ( const char ∗ __str, FILE ∗ __stream )

Write the string pointed to by str to stream stream.

Returns 0 on success and EOF on error.

23.9.4.13 int fputs_P ( const char ∗ __str, FILE ∗ __stream )

Variant of fputs() where str resides in program memory.

23.9.4.14 size_t fread ( void ∗ __ptr, size_t __size, size_t __nmemb, FILE ∗ __stream )

Read nmemb objects, size bytes each, from stream, to the buffer pointed to by ptr.

Returns the number of objects successfully read, i. e. nmemb unless an input error occured or end-of-file was encoun-tered. feof() and ferror() must be used to distinguish between these two conditions.

23.9.4.15 int fscanf ( FILE ∗ __stream, const char ∗ __fmt, ... )

The function fscanf performs formatted input, reading the input data from stream.


158 CONTENTS

See vfscanf() for details.

23.9.4.16 int fscanf_P ( FILE ∗ __stream, const char ∗ __fmt, ... )

Variant of fscanf() using a fmt string in program memory.

23.9.4.17 size_t fwrite ( const void ∗ __ptr, size_t __size, size_t __nmemb, FILE ∗ __stream )

Write nmemb objects, size bytes each, to stream. The first byte of the first object is referenced by ptr.

Returns the number of objects successfully written, i. e. nmemb unless an output error occured.

23.9.4.18 char∗ gets ( char ∗ __str )

Similar to fgets() except that it will operate on stream stdin, and the trailing newline (if any) will not be stored in thestring. It is the caller’s responsibility to provide enough storage to hold the characters read.

23.9.4.19 int printf ( const char ∗ __fmt, ... )

The function printf performs formatted output to stream stdout. See vfprintf() for details.

23.9.4.20 int printf_P ( const char ∗ __fmt, ... )

Variant of printf() that uses a fmt string that resides in program memory.

23.9.4.21 int puts ( const char ∗ __str )

Write the string pointed to by str, and a trailing newline character, to stdout.

23.9.4.22 int puts_P ( const char ∗ __str )

Variant of puts() where str resides in program memory.

23.9.4.23 int scanf ( const char ∗ __fmt, ... )

The function scanf performs formatted input from stream stdin.


23.9.4.24 int scanf_P ( const char ∗ __fmt, ... )

Variant of scanf() where fmt resides in program memory.

23.9.4.25 int snprintf ( char ∗ __s, size_t __n, const char ∗ __fmt, ... )

Like sprintf(), but instead of assuming s to be of infinite size, no more than n characters (including the trailing NULcharacter) will be converted to s.

Returns the number of characters that would have been written to s if there were enough space.

23.9.4.26 int snprintf_P ( char ∗ __s, size_t __n, const char ∗ __fmt, ... )

Variant of snprintf() that uses a fmt string that resides in program memory.

23.9.4.27 int sprintf ( char ∗ __s, const char ∗ __fmt, ... )

Variant of printf() that sends the formatted characters to string s.



23.9.4.28 int sprintf_P ( char ∗ __s, const char ∗ __fmt, ... )

Variant of sprintf() that uses a fmt string that resides in program memory.

23.9.4.29 int sscanf ( const char ∗ __buf, const char ∗ __fmt, ... )

The function sscanf performs formatted input, reading the input data from the buffer pointed to by buf.


23.9.4.30 int sscanf_P ( const char ∗ __buf, const char ∗ __fmt, ... )

Variant of sscanf() using a fmt string in program memory.

23.9.4.31 int ungetc ( int __c, FILE ∗ __stream )

The ungetc() function pushes the character c (converted to an unsigned char) back onto the input stream pointed to bystream. The pushed-back character will be returned by a subsequent read on the stream.

Currently, only a single character can be pushed back onto the stream.

The ungetc() function returns the character pushed back after the conversion, or EOF if the operation fails. If the valueof the argument c character equals EOF, the operation will fail and the stream will remain unchanged.

23.9.4.32 int vfprintf ( FILE ∗ __stream, const char ∗ __fmt, va_list __ap )

vfprintf is the central facility of the printf family of functions. It outputs values to stream under control of aformat string passed in fmt. The actual values to print are passed as a variable argument list ap.

vfprintf returns the number of characters written to stream, or EOF in case of an error. Currently, this will onlyhappen if stream has not been opened with write intent.

The format string is composed of zero or more directives: ordinary characters (not %), which are copied unchanged tothe output stream; and conversion specifications, each of which results in fetching zero or more subsequent arguments.Each conversion specification is introduced by the % character. The arguments must properly correspond (after typepromotion) with the conversion specifier. After the %, the following appear in sequence:

• Zero or more of the following flags:

– # The value should be converted to an "alternate form". For c, d, i, s, and u conversions, this option has noeffect. For o conversions, the precision of the number is increased to force the first character of the outputstring to a zero (except if a zero value is printed with an explicit precision of zero). For x and X conversions,a non-zero result has the string ‘0x’ (or ‘0X’ for X conversions) prepended to it.

– 0 (zero) Zero padding. For all conversions, the converted value is padded on the left with zeros rather thanblanks. If a precision is given with a numeric conversion (d, i, o, u, i, x, and X), the 0 flag is ignored.

– - A negative field width flag; the converted value is to be left adjusted on the field boundary. The convertedvalue is padded on the right with blanks, rather than on the left with blanks or zeros. A - overrides a 0 if bothare given.

– ’ ’ (space) A blank should be left before a positive number produced by a signed conversion (d, or i).

– + A sign must always be placed before a number produced by a signed conversion. A + overrides a spaceif both are used.

• An optional decimal digit string specifying a minimum field width. If the converted value has fewer characters thanthe field width, it will be padded with spaces on the left (or right, if the left-adjustment flag has been given) to fillout the field width.

• An optional precision, in the form of a period . followed by an optional digit string. If the digit string is omitted, theprecision is taken as zero. This gives the minimum number of digits to appear for d, i, o, u, x, and X conversions,or the maximum number of characters to be printed from a string for s conversions.


160 CONTENTS

• An optional l or h length modifier, that specifies that the argument for the d, i, o, u, x, or X conversion is a "longint" rather than int. The h is ignored, as "short int" is equivalent to int.

• A character that specifies the type of conversion to be applied.

The conversion specifiers and their meanings are:

• diouxX The int (or appropriate variant) argument is converted to signed decimal (d and i), unsigned octal (o),unsigned decimal (u), or unsigned hexadecimal (x and X) notation. The letters "abcdef" are used for x conversions;the letters "ABCDEF" are used for X conversions. The precision, if any, gives the minimum number of digits thatmust appear; if the converted value requires fewer digits, it is padded on the left with zeros.

• p The void ∗ argument is taken as an unsigned integer, and converted similarly as a %#x command would do.

• c The int argument is converted to an "unsigned char", and the resulting character is written.

• s The "char ∗" argument is expected to be a pointer to an array of character type (pointer to a string). Char-acters from the array are written up to (but not including) a terminating NUL character; if a precision is specified,no more than the number specified are written. If a precision is given, no null character need be present; ifthe precision is not specified, or is greater than the size of the array, the array must contain a terminating NULcharacter.

• % A % is written. No argument is converted. The complete conversion specification is "%%".

• eE The double argument is rounded and converted in the format "[-]d.ddde±dd" where there is one digitbefore the decimal-point character and the number of digits after it is equal to the precision; if the precision ismissing, it is taken as 6; if the precision is zero, no decimal-point character appears. An E conversion uses theletter ’E’ (rather than ’e’) to introduce the exponent. The exponent always contains two digits; if the value iszero, the exponent is 00.

• fF The double argument is rounded and converted to decimal notation in the format "[-]ddd.ddd", wherethe number of digits after the decimal-point character is equal to the precision specification. If the precision ismissing, it is taken as 6; if the precision is explicitly zero, no decimal-point character appears. If a decimal pointappears, at least one digit appears before it.

• gG The double argument is converted in style f or e (or F or E for G conversions). The precision specifies thenumber of significant digits. If the precision is missing, 6 digits are given; if the precision is zero, it is treated as 1.Style e is used if the exponent from its conversion is less than -4 or greater than or equal to the precision. Trailingzeros are removed from the fractional part of the result; a decimal point appears only if it is followed by at leastone digit.

• S Similar to the s format, except the pointer is expected to point to a program-memory (ROM) string instead of aRAM string.

In no case does a non-existent or small field width cause truncation of a numeric field; if the result of a conversion iswider than the field width, the field is expanded to contain the conversion result.

Since the full implementation of all the mentioned features becomes fairly large, three different flavours of vfprintf()can be selected using linker options. The default vfprintf() implements all the mentioned functionality except floatingpoint conversions. A minimized version of vfprintf() is available that only implements the very basic integer and stringconversion facilities, but only the # additional option can be specified using conversion flags (these flags are parsedcorrectly from the format specification, but then simply ignored). This version can be requested using the followingcompiler options:

-Wl,-u,vfprintf -lprintf_min

If the full functionality including the floating point conversions is required, the following options should be used:



-Wl,-u,vfprintf -lprintf_flt -lm

Limitations:

• The specified width and precision can be at most 255.

Notes:

• For floating-point conversions, if you link default or minimized version of vfprintf(), the symbol ? will be outputand double argument will be skiped. So you output below will not be crashed. For default version the widthfield and the "pad to left" ( symbol minus ) option will work in this case.

• The hh length modifier is ignored (char argument is promouted to int). More exactly, this realization doesnot check the number of h symbols.

• But the ll length modifier will to abort the output, as this realization does not operate long long arguments.

• The variable width or precision field (an asterisk ∗ symbol) is not realized and will to abort the output.

23.9.4.33 int vfprintf_P ( FILE ∗ __stream, const char ∗ __fmt, va_list __ap )

Variant of vfprintf() that uses a fmt string that resides in program memory.

23.9.4.34 int vfscanf ( FILE ∗ stream, const char ∗ fmt, va_list ap )

Formatted input. This function is the heart of the scanf family of functions.

Characters are read from stream and processed in a way described by fmt. Conversion results will be assigned to theparameters passed via ap.

The format string fmt is scanned for conversion specifications. Anything that doesn’t comprise a conversion specificationis taken as text that is matched literally against the input. White space in the format string will match any white space inthe data (including none), all other characters match only itself. Processing is aborted as soon as the data and formatstring no longer match, or there is an error or end-of-file condition on stream.

Most conversions skip leading white space before starting the actual conversion.

Conversions are introduced with the character %. Possible options can follow the %:

• a ∗ indicating that the conversion should be performed but the conversion result is to be discarded; no parameterswill be processed from ap,

• the character h indicating that the argument is a pointer to short int (rather than int),

• the 2 characters hh indicating that the argument is a pointer to char (rather than int).

• the character l indicating that the argument is a pointer to long int (rather than int, for integer type conver-sions), or a pointer to double (for floating point conversions),

In addition, a maximal field width may be specified as a nonzero positive decimal integer, which will restrict the conver-sion to at most this many characters from the input stream. This field width is limited to at most 255 characters which isalso the default value (except for the c conversion that defaults to 1).

The following conversion flags are supported:

• % Matches a literal % character. This is not a conversion.

• d Matches an optionally signed decimal integer; the next pointer must be a pointer to int.

• i Matches an optionally signed integer; the next pointer must be a pointer to int. The integer is read in base 16if it begins with 0x or 0X, in base 8 if it begins with 0, and in base 10 otherwise. Only characters that correspondto the base are used.


162 CONTENTS

• o Matches an octal integer; the next pointer must be a pointer to unsigned int.

• u Matches an optionally signed decimal integer; the next pointer must be a pointer to unsigned int.

• x Matches an optionally signed hexadecimal integer; the next pointer must be a pointer to unsigned int.

• f Matches an optionally signed floating-point number; the next pointer must be a pointer to float.

• e, g, F, E, G Equivalent to f.

• s Matches a sequence of non-white-space characters; the next pointer must be a pointer to char, and the arraymust be large enough to accept all the sequence and the terminating NUL character. The input string stops atwhite space or at the maximum field width, whichever occurs first.

• c Matches a sequence of width count characters (default 1); the next pointer must be a pointer to char, andthere must be enough room for all the characters (no terminating NUL is added). The usual skip of leading whitespace is suppressed. To skip white space first, use an explicit space in the format.

• [ Matches a nonempty sequence of characters from the specified set of accepted characters; the next pointermust be a pointer to char, and there must be enough room for all the characters in the string, plus a terminatingNUL character. The usual skip of leading white space is suppressed. The string is to be made up of characters in(or not in) a particular set; the set is defined by the characters between the open bracket [ character and a closebracket ] character. The set excludes those characters if the first character after the open bracket is a circumflex ∧.To include a close bracket in the set, make it the first character after the open bracket or the circumflex; any otherposition will end the set. The hyphen character - is also special; when placed between two other characters, itadds all intervening characters to the set. To include a hyphen, make it the last character before the final closebracket. For instance, [∧]0-9-] means the set of everything except close bracket, zero through nine, andhyphen. The string ends with the appearance of a character not in the (or, with a circumflex, in) set or when thefield width runs out. Note that usage of this conversion enlarges the stack expense.

• p Matches a pointer value (as printed by p in printf()); the next pointer must be a pointer to void.

• n Nothing is expected; instead, the number of characters consumed thus far from the input is stored through thenext pointer, which must be a pointer to int. This is not a conversion, although it can be suppressed with the ∗flag.

These functions return the number of input items assigned, which can be fewer than provided for, or even zero, inthe event of a matching failure. Zero indicates that, while there was input available, no conversions were assigned;typically this is due to an invalid input character, such as an alphabetic character for a d conversion. The valueEOF is returned if an input failure occurs before any conversion such as an end-of-file occurs. If an error orend-of-file occurs after conversion has begun, the number of conversions which were successfully completed isreturned.

By default, all the conversions described above are available except the floating-point conversions and the widthis limited to 255 characters. The float-point conversion will be available in the extended version provided by thelibrary libscanf_flt.a. Also in this case the width is not limited (exactly, it is limited to 65535 characters).To link a program against the extended version, use the following compiler flags in the link stage:

-Wl,-u,vfscanf -lscanf_flt -lm

A third version is available for environments that are tight on space. In addition to the restrictions of the standard one,this version implements no %[ specification. This version is provided in the library libscanf_min.a, and can berequested using the following options in the link stage:

-Wl,-u,vfscanf -lscanf_min -lm

23.9.4.35 int vfscanf_P ( FILE ∗ __stream, const char ∗ __fmt, va_list __ap )

Variant of vfscanf() using a fmt string in program memory.



23.9.4.36 int vprintf ( const char ∗ __fmt, va_list __ap )

The function vprintf performs formatted output to stream stdout, taking a variable argument list as in vfprintf().

See vfprintf() for details.

23.9.4.37 int vscanf ( const char ∗ __fmt, va_list __ap )

The function vscanf performs formatted input from stream stdin, taking a variable argument list as in vfscanf().


23.9.4.38 int vsnprintf ( char ∗ __s, size_t __n, const char ∗ __fmt, va_list ap )

Like vsprintf(), but instead of assuming s to be of infinite size, no more than n characters (including the trailingNUL character) will be converted to s.

Returns the number of characters that would have been written to s if there were enough space.

23.9.4.39 int vsnprintf_P ( char ∗ __s, size_t __n, const char ∗ __fmt, va_list ap )

Variant of vsnprintf() that uses a fmt string that resides in program memory.

23.9.4.40 int vsprintf ( char ∗ __s, const char ∗ __fmt, va_list ap )

Like sprintf() but takes a variable argument list for the arguments.

23.9.4.41 int vsprintf_P ( char ∗ __s, const char ∗ __fmt, va_list ap )

Variant of vsprintf() that uses a fmt string that resides in program memory.


164 CONTENTS

23.10 <stdlib.h>: General utilities

Data Structures

• struct div_t

• struct ldiv_t

Macros

• #define RAND_MAX 0x7FFF

Typedefs

• typedef int(∗ __compar_fn_t )(const void ∗, const void ∗)

Functions

• void abort (void) __ATTR_NORETURN__

• int abs (int __i)

• long labs (long __i)

• void ∗ bsearch (const void ∗__key, const void ∗__base, size_t __nmemb, size_t __size, int(∗__compar)(constvoid ∗, const void ∗))

• div_t div (int __num, int __denom) __asm__("__divmodhi4")

• ldiv_t ldiv (long __num, long __denom) __asm__("__divmodsi4")

• void qsort (void ∗__base, size_t __nmemb, size_t __size, __compar_fn_t __compar)

• long strtol (const char ∗__nptr, char ∗∗__endptr, int __base)

• unsigned long strtoul (const char ∗__nptr, char ∗∗__endptr, int __base)

• long atol (const char ∗__s) __ATTR_PURE__

• int atoi (const char ∗__s) __ATTR_PURE__

• void exit (int __status) __ATTR_NORETURN__

• void ∗ malloc (size_t __size) __ATTR_MALLOC__

• void free (void ∗__ptr)

• void ∗ calloc (size_t __nele, size_t __size) __ATTR_MALLOC__

• void ∗ realloc (void ∗__ptr, size_t __size) __ATTR_MALLOC__

• double strtod (const char ∗__nptr, char ∗∗__endptr)

• double atof (const char ∗__nptr)

• int rand (void)

• void srand (unsigned int __seed)

• int rand_r (unsigned long ∗__ctx)

Variables

• size_t __malloc_margin

• char ∗ __malloc_heap_start

• char ∗ __malloc_heap_end


23.10 <stdlib.h>: General utilities 165

Non-standard (i.e. non-ISO C) functions.

• char ∗ ltoa (long val, char ∗s, int radix)• char ∗ utoa (unsigned int val, char ∗s, int radix)• char ∗ ultoa (unsigned long val, char ∗s, int radix)• long random (void)• void srandom (unsigned long __seed)• long random_r (unsigned long ∗__ctx)• char ∗ itoa (int val, char ∗s, int radix)• #define RANDOM_MAX 0x7FFFFFFF

Conversion functions for double arguments.

Note that these functions are not located in the default library, libc.a, but in the mathematical library, libm.a. Sowhen linking the application, the -lm option needs to be specified.

• char ∗ dtostre (double __val, char ∗__s, unsigned char __prec, unsigned char __flags)• char ∗ dtostrf (double __val, signed char __width, unsigned char __prec, char ∗__s)• #define DTOSTR_ALWAYS_SIGN 0x01 /∗ put ’+’ or ’ ’ for positives ∗/• #define DTOSTR_PLUS_SIGN 0x02 /∗ put ’+’ rather than ’ ’ ∗/• #define DTOSTR_UPPERCASE 0x04 /∗ put ’E’ rather ’e’ ∗/• #define EXIT_SUCCESS 0• #define EXIT_FAILURE 1


#include <stdlib.h>

This file declares some basic C macros and functions as defined by the ISO standard, plus some AVR-specific exten-sions.


23.10.2.1 #define DTOSTR_ALWAYS_SIGN 0x01 /∗ put ’+’ or ’ ’ for positives ∗/

Bit value that can be passed in flags to dtostre().

23.10.2.2 #define DTOSTR_PLUS_SIGN 0x02 /∗ put ’+’ rather than ’ ’ ∗/


23.10.2.3 #define DTOSTR_UPPERCASE 0x04 /∗ put ’E’ rather ’e’ ∗/


23.10.2.4 #define EXIT_FAILURE 1

Unsuccessful termination for exit(); evaluates to a non-zero value.

23.10.2.5 #define EXIT_SUCCESS 0

Successful termination for exit(); evaluates to 0.


166 CONTENTS

23.10.2.6 #define RAND_MAX 0x7FFF

Highest number that can be generated by rand().

23.10.2.7 #define RANDOM_MAX 0x7FFFFFFF

Highest number that can be generated by random().


23.10.3.1 typedef int(∗ __compar_fn_t)(const void ∗, const void ∗)

Comparision function type for qsort(), just for convenience.


23.10.4.1 void abort ( void )

The abort() function causes abnormal program termination to occur. This realization disables interrupts and jumps to_exit() function with argument equal to 1. In the limited AVR environment, execution is effectively halted by entering aninfinite loop.

23.10.4.2 int abs ( int __i )

The abs() function computes the absolute value of the integer i.

Note

The abs() and labs() functions are builtins of gcc.

23.10.4.3 double atof ( const char ∗ nptr )

The atof() function converts the initial portion of the string pointed to by nptr to double representation.

It is equivalent to calling

strtod(nptr, (char **)0);

23.10.4.4 int atoi ( const char ∗ s )

Convert a string to an integer.

The atoi() function converts the initial portion of the string pointed to by s to integer representation. In contrast to

(int)strtol(s, (char **)NULL, 10);

this function does not detect overflow (errno is not changed and the result value is not predictable), uses smallermemory (flash and stack) and works more quickly.

23.10.4.5 long atol ( const char ∗ s )

Convert a string to a long integer.

The atol() function converts the initial portion of the string pointed to by s to long integer representation. In contrast to



strtol(s, (char **)NULL, 10);

this function does not detect overflow (errno is not changed and the result value is not predictable), uses smallermemory (flash and stack) and works more quickly.

23.10.4.6 void∗ bsearch ( const void ∗ __key, const void ∗ __base, size_t __nmemb, size_t __size, int(∗)(const void ∗, const void∗) __compar )

The bsearch() function searches an array of nmemb objects, the initial member of which is pointed to by base, for amember that matches the object pointed to by key. The size of each member of the array is specified by size.

The contents of the array should be in ascending sorted order according to the comparison function referenced bycompar. The compar routine is expected to have two arguments which point to the key object and to an arraymember, in that order, and should return an integer less than, equal to, or greater than zero if the key object is found,respectively, to be less than, to match, or be greater than the array member.

The bsearch() function returns a pointer to a matching member of the array, or a null pointer if no match is found. If twomembers compare as equal, which member is matched is unspecified.

23.10.4.7 void∗ calloc ( size_t __nele, size_t __size )

Allocate nele elements of size each. Identical to calling malloc() using nele ∗ size as argument, except theallocated memory will be cleared to zero.

23.10.4.8 div_t div ( int __num, int __denom )

The div() function computes the value num/denom and returns the quotient and remainder in a structure named div←↩_t that contains two int members named quot and rem.

23.10.4.9 char∗ dtostre ( double __val, char ∗ __s, unsigned char __prec, unsigned char __flags )

The dtostre() function converts the double value passed in val into an ASCII representation that will be stored unders. The caller is responsible for providing sufficient storage in s.

Conversion is done in the format "[-]d.ddde±dd" where there is one digit before the decimal-point character andthe number of digits after it is equal to the precision prec; if the precision is zero, no decimal-point character appears.If flags has the DTOSTRE_UPPERCASE bit set, the letter ’E’ (rather than ’e’ ) will be used to introduce theexponent. The exponent always contains two digits; if the value is zero, the exponent is "00".

If flags has the DTOSTRE_ALWAYS_SIGN bit set, a space character will be placed into the leading position forpositive numbers.

If flags has the DTOSTRE_PLUS_SIGN bit set, a plus sign will be used instead of a space character in this case.

The dtostre() function returns the pointer to the converted string s.

23.10.4.10 char∗ dtostrf ( double __val, signed char __width, unsigned char __prec, char ∗ __s )

The dtostrf() function converts the double value passed in val into an ASCII representationthat will be stored under s.The caller is responsible for providing sufficient storage in s.

Conversion is done in the format "[-]d.ddd". The minimum field width of the output string (including the possible’.’ and the possible sign for negative values) is given in width, and prec determines the number of digits after thedecimal sign. width is signed value, negative for left adjustment.

The dtostrf() function returns the pointer to the converted string s.


168 CONTENTS

23.10.4.11 void exit ( int __status )

The exit() function terminates the application. Since there is no environment to return to, status is ignored, and codeexecution will eventually reach an infinite loop, thereby effectively halting all code processing. Before entering the infiniteloop, interrupts are globally disabled.

In a C++ context, global destructors will be called before halting execution.

23.10.4.12 void free ( void ∗ __ptr )

The free() function causes the allocated memory referenced by ptr to be made available for future allocations. If ptris NULL, no action occurs.

23.10.4.13 char∗ itoa ( int val, char ∗ s, int radix )

Convert an integer to a string.

The function itoa() converts the integer value from val into an ASCII representation that will be stored under s. Thecaller is responsible for providing sufficient storage in s.

Note

The minimal size of the buffer s depends on the choice of radix. For example, if the radix is 2 (binary), you needto supply a buffer with a minimal length of 8 ∗ sizeof (int) + 1 characters, i.e. one character for each bit plus onefor the string terminator. Using a larger radix will require a smaller minimal buffer size.

Warning

If the buffer is too small, you risk a buffer overflow.

Conversion is done using the radix as base, which may be a number between 2 (binary conversion) and up to 36. Ifradix is greater than 10, the next digit after ’9’ will be the letter ’a’.

If radix is 10 and val is negative, a minus sign will be prepended.

The itoa() function returns the pointer passed as s.

23.10.4.14 long labs ( long __i )

The labs() function computes the absolute value of the long integer i.

Note

The abs() and labs() functions are builtins of gcc.

23.10.4.15 ldiv_t ldiv ( long __num, long __denom )

The ldiv() function computes the value num/denom and returns the quotient and remainder in a structure namedldiv_t that contains two long integer members named quot and rem.

23.10.4.16 char∗ ltoa ( long val, char ∗ s, int radix )

Convert a long integer to a string.

The function ltoa() converts the long integer value from val into an ASCII representation that will be stored under s.The caller is responsible for providing sufficient storage in s.



Note

The minimal size of the buffer s depends on the choice of radix. For example, if the radix is 2 (binary), you needto supply a buffer with a minimal length of 8 ∗ sizeof (long int) + 1 characters, i.e. one character for each bit plusone for the string terminator. Using a larger radix will require a smaller minimal buffer size.

Warning



If radix is 10 and val is negative, a minus sign will be prepended.

The ltoa() function returns the pointer passed as s.

23.10.4.17 void∗ malloc ( size_t __size )

The malloc() function allocates size bytes of memory. If malloc() fails, a NULL pointer is returned.

Note that malloc() does not initialize the returned memory to zero bytes.

See the chapter about malloc() usage for implementation details.

23.10.4.18 void qsort ( void ∗ __base, size_t __nmemb, size_t __size, __compar_fn_t __compar )

The qsort() function is a modified partition-exchange sort, or quicksort.

The qsort() function sorts an array of nmemb objects, the initial member of which is pointed to by base. The size of eachobject is specified by size. The contents of the array base are sorted in ascending order according to a comparisonfunction pointed to by compar, which requires two arguments pointing to the objects being compared.

The comparison function must return an integer less than, equal to, or greater than zero if the first argument is consideredto be respectively less than, equal to, or greater than the second.

23.10.4.19 int rand ( void )

The rand() function computes a sequence of pseudo-random integers in the range of 0 to RAND_MAX (as defined bythe header file <stdlib.h>).

The srand() function sets its argument seed as the seed for a new sequence of pseudo-random numbers to be returnedby rand(). These sequences are repeatable by calling srand() with the same seed value.

If no seed value is provided, the functions are automatically seeded with a value of 1.

In compliance with the C standard, these functions operate on int arguments. Since the underlying algorithm alreadyuses 32-bit calculations, this causes a loss of precision. See random() for an alternate set of functions that retainsfull 32-bit precision.

23.10.4.20 int rand_r ( unsigned long ∗ __ctx )

Variant of rand() that stores the context in the user-supplied variable located at ctx instead of a static library variableso the function becomes re-entrant.

23.10.4.21 long random ( void )

The random() function computes a sequence of pseudo-random integers in the range of 0 to RANDOM_MAX (as definedby the header file <stdlib.h>).

The srandom() function sets its argument seed as the seed for a new sequence of pseudo-random numbers to bereturned by rand(). These sequences are repeatable by calling srandom() with the same seed value.


170 CONTENTS

If no seed value is provided, the functions are automatically seeded with a value of 1.

23.10.4.22 long random_r ( unsigned long ∗ __ctx )

Variant of random() that stores the context in the user-supplied variable located at ctx instead of a static library variableso the function becomes re-entrant.

23.10.4.23 void∗ realloc ( void ∗ __ptr, size_t __size )

The realloc() function tries to change the size of the region allocated at ptr to the new size value. It returns a pointerto the new region. The returned pointer might be the same as the old pointer, or a pointer to a completely differentregion.

The contents of the returned region up to either the old or the new size value (whatever is less) will be identical to thecontents of the old region, even in case a new region had to be allocated.

It is acceptable to pass ptr as NULL, in which case realloc() will behave identical to malloc().

If the new memory cannot be allocated, realloc() returns NULL, and the region at ptr will not be changed.

23.10.4.24 void srand ( unsigned int __seed )

Pseudo-random number generator seeding; see rand().

23.10.4.25 void srandom ( unsigned long __seed )

Pseudo-random number generator seeding; see random().

23.10.4.26 double strtod ( const char ∗ nptr, char ∗∗ endptr )

The strtod() function converts the initial portion of the string pointed to by nptr to double representation.

The expected form of the string is an optional plus ( ’+’ ) or minus sign ( ’-’ ) followed by a sequence of digitsoptionally containing a decimal-point character, optionally followed by an exponent. An exponent consists of an ’E’ or’e’, followed by an optional plus or minus sign, followed by a sequence of digits.

Leading white-space characters in the string are skipped.

The strtod() function returns the converted value, if any.

If endptr is not NULL, a pointer to the character after the last character used in the conversion is stored in the locationreferenced by endptr.

If no conversion is performed, zero is returned and the value of nptr is stored in the location referenced by endptr.

If the correct value would cause overflow, plus or minus INFINITY is returned (according to the sign of the value),and ERANGE is stored in errno. If the correct value would cause underflow, zero is returned and ERANGE is stored inerrno.

23.10.4.27 long strtol ( const char ∗ __nptr, char ∗∗ __endptr, int __base )

The strtol() function converts the string in nptr to a long value. The conversion is done according to the given base,which must be between 2 and 36 inclusive, or be the special value 0.

The string may begin with an arbitrary amount of white space (as determined by isspace()) followed by a single optional’+’ or ’-’ sign. If base is zero or 16, the string may then include a "0x" prefix, and the number will be read inbase 16; otherwise, a zero base is taken as 10 (decimal) unless the next character is ’0’, in which case it is taken as8 (octal).

The remainder of the string is converted to a long value in the obvious manner, stopping at the first character which isnot a valid digit in the given base. (In bases above 10, the letter ’A’ in either upper or lower case represents 10, ’B’



represents 11, and so forth, with ’Z’ representing 35.)

If endptr is not NULL, strtol() stores the address of the first invalid character in ∗endptr. If there were no digits at all,however, strtol() stores the original value of nptr in endptr. (Thus, if ∗nptr is not ’\0’ but ∗∗endptr is ’\0’on return, the entire string was valid.)

The strtol() function returns the result of the conversion, unless the value would underflow or overflow. If no conversioncould be performed, 0 is returned. If an overflow or underflow occurs, errno is set to ERANGE and the function returnvalue is clamped to LONG_MIN or LONG_MAX, respectively.

23.10.4.28 unsigned long strtoul ( const char ∗ __nptr, char ∗∗ __endptr, int __base )

The strtoul() function converts the string in nptr to an unsigned long value. The conversion is done according to thegiven base, which must be between 2 and 36 inclusive, or be the special value 0.

The string may begin with an arbitrary amount of white space (as determined by isspace()) followed by a single optional’+’ or ’-’ sign. If base is zero or 16, the string may then include a "0x" prefix, and the number will be read inbase 16; otherwise, a zero base is taken as 10 (decimal) unless the next character is ’0’, in which case it is taken as8 (octal).

The remainder of the string is converted to an unsigned long value in the obvious manner, stopping at the first characterwhich is not a valid digit in the given base. (In bases above 10, the letter ’A’ in either upper or lower case represents10, ’B’ represents 11, and so forth, with ’Z’ representing 35.)

If endptr is not NULL, strtoul() stores the address of the first invalid character in ∗endptr. If there were no digitsat all, however, strtoul() stores the original value of nptr in endptr. (Thus, if ∗nptr is not ’\0’ but ∗∗endptr is’\0’ on return, the entire string was valid.)

The strtoul() function return either the result of the conversion or, if there was a leading minus sign, the negation ofthe result of the conversion, unless the original (non-negated) value would overflow; in the latter case, strtoul() returnsULONG_MAX, and errno is set to ERANGE. If no conversion could be performed, 0 is returned.

23.10.4.29 char∗ ultoa ( unsigned long val, char ∗ s, int radix )

Convert an unsigned long integer to a string.

The function ultoa() converts the unsigned long integer value from val into an ASCII representation that will be storedunder s. The caller is responsible for providing sufficient storage in s.

Note

The minimal size of the buffer s depends on the choice of radix. For example, if the radix is 2 (binary), you needto supply a buffer with a minimal length of 8 ∗ sizeof (unsigned long int) + 1 characters, i.e. one character for eachbit plus one for the string terminator. Using a larger radix will require a smaller minimal buffer size.

Warning



The ultoa() function returns the pointer passed as s.

23.10.4.30 char∗ utoa ( unsigned int val, char ∗ s, int radix )

Convert an unsigned integer to a string.

The function utoa() converts the unsigned integer value from val into an ASCII representation that will be stored unders. The caller is responsible for providing sufficient storage in s.


172 CONTENTS

Note

The minimal size of the buffer s depends on the choice of radix. For example, if the radix is 2 (binary), you needto supply a buffer with a minimal length of 8 ∗ sizeof (unsigned int) + 1 characters, i.e. one character for each bitplus one for the string terminator. Using a larger radix will require a smaller minimal buffer size.

Warning



The utoa() function returns the pointer passed as s.

23.10.5 Variable Documentation

23.10.5.1 char∗ __malloc_heap_end

malloc() tunable.

23.10.5.2 char∗ __malloc_heap_start

malloc() tunable.

23.10.5.3 size_t __malloc_margin

malloc() tunable.


23.11 <string.h>: Strings 173

23.11 <string.h>: Strings

Macros

• #define _FFS(x)

Functions

• int ffs (int __val)

• int ffsl (long __val)

• __extension__ int ffsll (long long __val)

• void ∗ memccpy (void ∗, const void ∗, int, size_t)

• void ∗ memchr (const void ∗, int, size_t) __ATTR_PURE__

• int memcmp (const void ∗, const void ∗, size_t) __ATTR_PURE__

• void ∗ memcpy (void ∗, const void ∗, size_t)

• void ∗ memmem (const void ∗, size_t, const void ∗, size_t) __ATTR_PURE__

• void ∗ memmove (void ∗, const void ∗, size_t)

• void ∗ memrchr (const void ∗, int, size_t) __ATTR_PURE__

• void ∗ memset (void ∗, int, size_t)

• int strcasecmp (const char ∗, const char ∗) __ATTR_PURE__

• char ∗ strcasestr (const char ∗, const char ∗) __ATTR_PURE__

• char ∗ strcat (char ∗, const char ∗)• char ∗ strchr (const char ∗, int) __ATTR_PURE__

• char ∗ strchrnul (const char ∗, int) __ATTR_PURE__

• int strcmp (const char ∗, const char ∗) __ATTR_PURE__

• char ∗ strcpy (char ∗, const char ∗)• size_t strcspn (const char ∗__s, const char ∗__reject) __ATTR_PURE__

• char ∗ strdup (const char ∗s1)

• size_t strlcat (char ∗, const char ∗, size_t)

• size_t strlcpy (char ∗, const char ∗, size_t)

• size_t strlen (const char ∗) __ATTR_PURE__

• char ∗ strlwr (char ∗)• int strncasecmp (const char ∗, const char ∗, size_t) __ATTR_PURE__

• char ∗ strncat (char ∗, const char ∗, size_t)

• int strncmp (const char ∗, const char ∗, size_t) __ATTR_PURE__

• char ∗ strncpy (char ∗, const char ∗, size_t)

• size_t strnlen (const char ∗, size_t) __ATTR_PURE__

• char ∗ strpbrk (const char ∗__s, const char ∗__accept) __ATTR_PURE__

• char ∗ strrchr (const char ∗, int) __ATTR_PURE__

• char ∗ strrev (char ∗)• char ∗ strsep (char ∗∗, const char ∗)• size_t strspn (const char ∗__s, const char ∗__accept) __ATTR_PURE__

• char ∗ strstr (const char ∗, const char ∗) __ATTR_PURE__

• char ∗ strtok (char ∗, const char ∗)• char ∗ strtok_r (char ∗, const char ∗, char ∗∗)• char ∗ strupr (char ∗)


174 CONTENTS


#include <string.h>

The string functions perform string operations on NULL terminated strings.

Note

If the strings you are working on resident in program space (flash), you will need to use the string functionsdescribed in <avr/pgmspace.h>: Program Space Utilities.


23.11.2.1 #define _FFS( x )

This macro finds the first (least significant) bit set in the input value.

This macro is very similar to the function ffs() except that it evaluates its argument at compile-time, so it should onlybe applied to compile-time constant expressions where it will reduce to a constant itself. Application of this macro toexpressions that are not constant at compile-time is not recommended, and might result in a huge amount of codegenerated.

Returns

The _FFS() macro returns the position of the first (least significant) bit set in the word val, or 0 if no bits are set.The least significant bit is position 1. Only 16 bits of argument are evaluted.


23.11.3.1 int ffs ( int val )

This function finds the first (least significant) bit set in the input value.

Returns

The ffs() function returns the position of the first (least significant) bit set in the word val, or 0 if no bits are set. Theleast significant bit is position 1.

Note

For expressions that are constant at compile time, consider using the _FFS macro instead.

23.11.3.2 int ffsl ( long __val )

Same as ffs(), for an argument of type long.

23.11.3.3 int ffsll ( long long __val )

Same as ffs(), for an argument of type long long.

23.11.3.4 void ∗ memccpy ( void ∗ dest, const void ∗ src, int val, size_t len )

Copy memory area.

The memccpy() function copies no more than len bytes from memory area src to memory area dest, stopping whenthe character val is found.



Returns

The memccpy() function returns a pointer to the next character in dest after val, or NULL if val was not foundin the first len characters of src.

23.11.3.5 void ∗ memchr ( const void ∗ src, int val, size_t len )

Scan memory for a character.

The memchr() function scans the first len bytes of the memory area pointed to by src for the character val. The first byteto match val (interpreted as an unsigned character) stops the operation.

Returns

The memchr() function returns a pointer to the matching byte or NULL if the character does not occur in the givenmemory area.

23.11.3.6 int memcmp ( const void ∗ s1, const void ∗ s2, size_t len )

Compare memory areas.

The memcmp() function compares the first len bytes of the memory areas s1 and s2. The comparision is performedusing unsigned char operations.

Returns

The memcmp() function returns an integer less than, equal to, or greater than zero if the first len bytes of s1 isfound, respectively, to be less than, to match, or be greater than the first len bytes of s2.

Note

Be sure to store the result in a 16 bit variable since you may get incorrect results if you use an unsigned char orchar due to truncation.

Warning

This function is not -mint8 compatible, although if you only care about testing for equality, this function should besafe to use.

23.11.3.7 void ∗ memcpy ( void ∗ dest, const void ∗ src, size_t len )

Copy a memory area.

The memcpy() function copies len bytes from memory area src to memory area dest. The memory areas may notoverlap. Use memmove() if the memory areas do overlap.

Returns

The memcpy() function returns a pointer to dest.

23.11.3.8 void ∗ memmem ( const void ∗ s1, size_t len1, const void ∗ s2, size_t len2 )

The memmem() function finds the start of the first occurrence of the substring s2 of length len2 in the memory areas1 of length len1.

Returns

The memmem() function returns a pointer to the beginning of the substring, or NULL if the substring is not found.If len2 is zero, the function returns s1.


176 CONTENTS

23.11.3.9 void ∗ memmove ( void ∗ dest, const void ∗ src, size_t len )

Copy memory area.

The memmove() function copies len bytes from memory area src to memory area dest. The memory areas may overlap.

Returns

The memmove() function returns a pointer to dest.

23.11.3.10 void ∗ memrchr ( const void ∗ src, int val, size_t len )

The memrchr() function is like the memchr() function, except that it searches backwards from the end of the len bytespointed to by src instead of forwards from the front. (Glibc, GNU extension.)

Returns

The memrchr() function returns a pointer to the matching byte or NULL if the character does not occur in the givenmemory area.

23.11.3.11 void ∗ memset ( void ∗ dest, int val, size_t len )

Fill memory with a constant byte.

The memset() function fills the first len bytes of the memory area pointed to by dest with the constant byte val.

Returns

The memset() function returns a pointer to the memory area dest.

23.11.3.12 int strcasecmp ( const char ∗ s1, const char ∗ s2 )

Compare two strings ignoring case.

The strcasecmp() function compares the two strings s1 and s2, ignoring the case of the characters.

Returns

The strcasecmp() function returns an integer less than, equal to, or greater than zero if s1 is found, respectively,to be less than, to match, or be greater than s2. A consequence of the ordering used by strcasecmp() is that ifs1 is an initial substring of s2, then s1 is considered to be "less than" s2.

23.11.3.13 char ∗ strcasestr ( const char ∗ s1, const char ∗ s2 )

The strcasestr() function finds the first occurrence of the substring s2 in the string s1. This is like strstr(), except that itignores case of alphabetic symbols in searching for the substring. (Glibc, GNU extension.)

Returns

The strcasestr() function returns a pointer to the beginning of the substring, or NULL if the substring is not found.If s2 points to a string of zero length, the function returns s1.

23.11.3.14 char ∗ strcat ( char ∗ dest, const char ∗ src )

Concatenate two strings.

The strcat() function appends the src string to the dest string overwriting the ’\0’ character at the end of dest, and thenadds a terminating ’\0’ character. The strings may not overlap, and the dest string must have enough space for theresult.



Returns

The strcat() function returns a pointer to the resulting string dest.

23.11.3.15 char ∗ strchr ( const char ∗ src, int val )

Locate character in string.

The strchr() function returns a pointer to the first occurrence of the character val in the string src.

Here "character" means "byte" - these functions do not work with wide or multi-byte characters.

Returns

The strchr() function returns a pointer to the matched character or NULL if the character is not found.

23.11.3.16 char ∗ strchrnul ( const char ∗ s, int c )

The strchrnul() function is like strchr() except that if c is not found in s, then it returns a pointer to the null byte at theend of s, rather than NULL. (Glibc, GNU extension.)

Returns

The strchrnul() function returns a pointer to the matched character, or a pointer to the null byte at the end of s (i.e.,s+strlen(s)) if the character is not found.

23.11.3.17 int strcmp ( const char ∗ s1, const char ∗ s2 )

Compare two strings.

The strcmp() function compares the two strings s1 and s2.

Returns

The strcmp() function returns an integer less than, equal to, or greater than zero if s1 is found, respectively, to beless than, to match, or be greater than s2. A consequence of the ordering used by strcmp() is that if s1 is aninitial substring of s2, then s1 is considered to be "less than" s2.

23.11.3.18 char ∗ strcpy ( char ∗ dest, const char ∗ src )

Copy a string.

The strcpy() function copies the string pointed to by src (including the terminating ’\0’ character) to the array pointed toby dest. The strings may not overlap, and the destination string dest must be large enough to receive the copy.

Returns

The strcpy() function returns a pointer to the destination string dest.

Note

If the destination string of a strcpy() is not large enough (that is, if the programmer was stupid/lazy, and failed tocheck the size before copying) then anything might happen. Overflowing fixed length strings is a favourite crackertechnique.


178 CONTENTS

23.11.3.19 size_t strcspn ( const char ∗ s, const char ∗ reject )

The strcspn() function calculates the length of the initial segment of s which consists entirely of characters not inreject.

Returns

The strcspn() function returns the number of characters in the initial segment of s which are not in the stringreject. The terminating zero is not considered as a part of string.

23.11.3.20 char ∗ strdup ( const char ∗ s1 )

Duplicate a string.

The strdup() function allocates memory and copies into it the string addressed by s1, including the terminating nullcharacter.

Warning

The strdup() function calls malloc() to allocate the memory for the duplicated string! The user is responsible forfreeing the memory by calling free().

Returns

The strdup() function returns a pointer to the resulting string dest. If malloc() cannot allocate enough storage forthe string, strdup() will return NULL.

Warning

Be sure to check the return value of the strdup() function to make sure that the function has succeeded in allocatingthe memory!

23.11.3.21 size_t strlcat ( char ∗ dst, const char ∗ src, size_t siz )


Appends src to string dst of size siz (unlike strncat(), siz is the full size of dst, not space left). At most siz-1 characterswill be copied. Always NULL terminates (unless siz <= strlen(dst)).

Returns

The strlcat() function returns strlen(src) + MIN(siz, strlen(initial dst)). If retval >= siz, truncation occurred.

Appends src to string dst of size siz (unlike strncat(), siz is the full size of dst, not space left). At most siz-1characters will be copied. Always NULL terminates (unless siz <= strlen(dst)).

Returns

The strlcat() function returns strlen(src) + MIN(siz, strlen(initial dst)). If retval >= siz, truncation occurred.

23.11.3.22 size_t strlcpy ( char ∗ dst, const char ∗ src, size_t siz )

Copy a string.

Copy src to string dst of size siz. At most siz-1 characters will be copied. Always NULL terminates (unless siz == 0).



Returns

The strlcpy() function returns strlen(src). If retval >= siz, truncation occurred.

Copy src to string dst of size siz. At most siz-1 characters will be copied. Always NULL terminates (unless siz== 0).

Returns

The strlcpy() function returns strlen(src). If retval >= siz, truncation occurred.

23.11.3.23 size_t strlen ( const char ∗ src )

Calculate the length of a string.

The strlen() function calculates the length of the string src, not including the terminating ’\0’ character.

Returns

The strlen() function returns the number of characters in src.

23.11.3.24 char ∗ strlwr ( char ∗ s )

Convert a string to lower case.

The strlwr() function will convert a string to lower case. Only the upper case alphabetic characters [A .. Z] are converted.Non-alphabetic characters will not be changed.

Returns

The strlwr() function returns a pointer to the converted string.

23.11.3.25 int strncasecmp ( const char ∗ s1, const char ∗ s2, size_t len )


The strncasecmp() function is similar to strcasecmp(), except it only compares the first len characters of s1.

Returns

The strncasecmp() function returns an integer less than, equal to, or greater than zero if s1 (or the first len bytesthereof) is found, respectively, to be less than, to match, or be greater than s2. A consequence of the orderingused by strncasecmp() is that if s1 is an initial substring of s2, then s1 is considered to be "less than" s2.

23.11.3.26 char ∗ strncat ( char ∗ dest, const char ∗ src, size_t len )


The strncat() function is similar to strcat(), except that only the first n characters of src are appended to dest.

Returns

The strncat() function returns a pointer to the resulting string dest.


180 CONTENTS

23.11.3.27 int strncmp ( const char ∗ s1, const char ∗ s2, size_t len )

Compare two strings.

The strncmp() function is similar to strcmp(), except it only compares the first (at most) n characters of s1 and s2.

Returns

The strncmp() function returns an integer less than, equal to, or greater than zero if s1 (or the first n bytes thereof)is found, respectively, to be less than, to match, or be greater than s2.

23.11.3.28 char ∗ strncpy ( char ∗ dest, const char ∗ src, size_t len )

Copy a string.

The strncpy() function is similar to strcpy(), except that not more than n bytes of src are copied. Thus, if there is no nullbyte among the first n bytes of src, the result will not be null-terminated.

In the case where the length of src is less than that of n, the remainder of dest will be padded with nulls.

Returns

The strncpy() function returns a pointer to the destination string dest.

23.11.3.29 size_t strnlen ( const char ∗ src, size_t len )

Determine the length of a fixed-size string.

The strnlen function returns the number of characters in the string pointed to by src, not including the terminating ’\0’character, but at most len. In doing this, strnlen looks only at the first len characters at src and never beyond src+len.

Returns

The strnlen function returns strlen(src), if that is less than len, or len if there is no ’\0’ character among the first lencharacters pointed to by src.

23.11.3.30 char ∗ strpbrk ( const char ∗ s, const char ∗ accept )

The strpbrk() function locates the first occurrence in the string s of any of the characters in the string accept.

Returns

The strpbrk() function returns a pointer to the character in s that matches one of the characters in accept, orNULL if no such character is found. The terminating zero is not considered as a part of string: if one or both argsare empty, the result will NULL.

23.11.3.31 char ∗ strrchr ( const char ∗ src, int val )

Locate character in string.

The strrchr() function returns a pointer to the last occurrence of the character val in the string src.

Here "character" means "byte" - these functions do not work with wide or multi-byte characters.

Returns

The strrchr() function returns a pointer to the matched character or NULL if the character is not found.



23.11.3.32 char ∗ strrev ( char ∗ s )

Reverse a string.

The strrev() function reverses the order of the string.

Returns

The strrev() function returns a pointer to the beginning of the reversed string.

23.11.3.33 char ∗ strsep ( char ∗∗ sp, const char ∗ delim )

Parse a string into tokens.

The strsep() function locates, in the string referenced by ∗sp, the first occurrence of any character in the string delim(or the terminating ’\0’ character) and replaces it with a ’\0’. The location of the next character after the delimitercharacter (or NULL, if the end of the string was reached) is stored in ∗sp. An “empty” field, i.e. one caused by twoadjacent delimiter characters, can be detected by comparing the location referenced by the pointer returned in ∗sp to’\0’.

Returns

The strsep() function returns a pointer to the original value of ∗sp. If ∗sp is initially NULL, strsep() returns NULL.

23.11.3.34 size_t strspn ( const char ∗ s, const char ∗ accept )

The strspn() function calculates the length of the initial segment of s which consists entirely of characters in accept.

Returns

The strspn() function returns the number of characters in the initial segment of s which consist only of charactersfrom accept. The terminating zero is not considered as a part of string.

23.11.3.35 char ∗ strstr ( const char ∗ s1, const char ∗ s2 )

Locate a substring.

The strstr() function finds the first occurrence of the substring s2 in the string s1. The terminating ’\0’ characters arenot compared.

Returns

The strstr() function returns a pointer to the beginning of the substring, or NULL if the substring is not found. If s2points to a string of zero length, the function returns s1.

23.11.3.36 char ∗ strtok ( char ∗ s, const char ∗ delim )

Parses the string s into tokens.

strtok parses the string s into tokens. The first call to strtok should have s as its first argument. Subsequent calls shouldhave the first argument set to NULL. If a token ends with a delimiter, this delimiting character is overwritten with a ’\0’and a pointer to the next character is saved for the next call to strtok. The delimiter string delim may be different for eachcall.

Returns

The strtok() function returns a pointer to the next token or NULL when no more tokens are found.


182 CONTENTS

Note

strtok() is NOT reentrant. For a reentrant version of this function see strtok_r().

23.11.3.37 char ∗ strtok_r ( char ∗ string, const char ∗ delim, char ∗∗ last )

Parses string into tokens.

strtok_r parses string into tokens. The first call to strtok_r should have string as its first argument. Subsequent callsshould have the first argument set to NULL. If a token ends with a delimiter, this delimiting character is overwritten with a’\0’ and a pointer to the next character is saved for the next call to strtok_r. The delimiter string delim may be differentfor each call. last is a user allocated char∗ pointer. It must be the same while parsing the same string. strtok_r is areentrant version of strtok().

Returns

The strtok_r() function returns a pointer to the next token or NULL when no more tokens are found.

23.11.3.38 char ∗ strupr ( char ∗ s )

Convert a string to upper case.

The strupr() function will convert a string to upper case. Only the lower case alphabetic characters [a .. z] are converted.Non-alphabetic characters will not be changed.

Returns

The strupr() function returns a pointer to the converted string. The pointer is the same as that passed in since theoperation is perform in place.


23.12 <time.h>: Time 183

23.12 <time.h>: Time

Data Structures

• struct tm• struct week_date

Macros

• #define CLOCKS_PER_SEC ((clock_t) _CLOCKS_PER_SEC_)• #define ONE_HOUR 3600• #define ONE_DEGREE 3600• #define ONE_DAY 86400• #define UNIX_OFFSET 946684800• #define NTP_OFFSET 3155673600

Typedefs

• typedef uint32_t time_t• typedef unsigned long clock_t

Enumerations

• enum _WEEK_DAYS_ {SUNDAY, MONDAY, TUESDAY, WEDNESDAY,THURSDAY, FRIDAY, SATURDAY }

• enum _MONTHS_ {JANUARY, FEBRUARY, MARCH, APRIL,MAY, JUNE, JULY, AUGUST,SEPTEMBER, OCTOBER, NOVEMBER, DECEMBER }

Functions

• time_t time (time_t ∗timer)• int32_t difftime (time_t time1, time_t time0)• clock_t clock (void)• time_t mktime (struct tm ∗timeptr)• time_t mk_gmtime (const struct tm ∗timeptr)• struct tm ∗ gmtime (const time_t ∗timer)• void gmtime_r (const time_t ∗timer, struct tm ∗timeptr)• struct tm ∗ localtime (const time_t ∗timer)• void localtime_r (const time_t ∗timer, struct tm ∗timeptr)• char ∗ asctime (const struct tm ∗timeptr)• void asctime_r (const struct tm ∗timeptr, char ∗buf)• char ∗ ctime (const time_t ∗timer)• void ctime_r (const time_t ∗timer, char ∗buf)• char ∗ isotime (const struct tm ∗tmptr)• void isotime_r (const struct tm ∗, char ∗)• size_t strftime (char ∗s, size_t maxsize, const char ∗format, const struct tm ∗timeptr)• void set_dst (int(∗)(const time_t ∗, int32_t ∗))


184 CONTENTS

• void set_zone (int32_t)• void set_system_time (time_t timestamp)• void system_tick (void)• uint8_t is_leap_year (int16_t year)• uint8_t month_length (int16_t year, uint8_t month)• uint8_t week_of_year (const struct tm ∗timeptr, uint8_t start)• uint8_t week_of_month (const struct tm ∗timeptr, uint8_t start)• struct week_date ∗ iso_week_date (int year, int yday)• void iso_week_date_r (int year, int yday, struct week_date ∗)• uint32_t fatfs_time (const struct tm ∗timeptr)• void set_position (int32_t latitude, int32_t longitude)• int16_t equation_of_time (const time_t ∗timer)• int32_t daylight_seconds (const time_t ∗timer)• time_t solar_noon (const time_t ∗timer)• time_t sun_rise (const time_t ∗timer)• time_t sun_set (const time_t ∗timer)• double solar_declination (const time_t ∗timer)• int8_t moon_phase (const time_t ∗timer)• unsigned long gm_sidereal (const time_t ∗timer)• unsigned long lm_sidereal (const time_t ∗timer)

Variables

• char ∗ _CLOCKS_PER_SEC_


#include <time.h>

Introduction to the Time functions

This file declares the time functions implemented in avr-libc.

The implementation aspires to conform with ISO/IEC 9899 (C90). However, due to limitations of the target processorand the nature of its development environment, a practical implementation must of necessity deviate from the standard.

Section 7.23.2.1 clock() The type clock_t, the macro CLOCKS_PER_SEC, and the function clock() are not implemented.We consider these items belong to operating system code, or to application code when no operating system is present.

Section 7.23.2.3 mktime() The standard specifies that mktime() should return (time_t) -1, if the time cannot be repre-sented. This implementation always returns a ’best effort’ representation.

Section 7.23.2.4 time() The standard specifies that time() should return (time_t) -1, if the time is not available. Since theapplication must initialize the time system, this functionality is not implemented.

Section 7.23.2.2, difftime() Due to the lack of a 64 bit double, the function difftime() returns a long integer. In most casesthis change will be invisible to the user, handled automatically by the compiler.

Section 7.23.1.4 struct tm Per the standard, struct tm->tm_isdst is greater than zero when Daylight Saving time is ineffect. This implementation further specifies that, when positive, the value of tm_isdst represents the amount time isadvanced during Daylight Saving time.

Section 7.23.3.5 strftime() Only the ’C’ locale is supported, therefore the modifiers ’E’ and ’O’ are ignored. The ’Z’conversion is also ignored, due to the lack of time zone name.


23.12 <time.h>: Time 185

In addition to the above departures from the standard, there are some behaviors which are different from what is oftenexpected, though allowed under the standard.

There is no ’platform standard’ method to obtain the current time, time zone, or daylight savings ’rules’ in the AVRenvironment. Therefore the application must initialize the time system with this information. The functions set_zone(),set_dst(), and set_system_time() are provided for initialization. Once initialized, system time is maintained by calling thefunction system_tick() at one second intervals.

Though not specified in the standard, it is often expected that time_t is a signed integer representing an offset in secondsfrom Midnight Jan 1 1970... i.e. ’Unix time’. This implementation uses an unsigned 32 bit integer offset from MidnightJan 1 2000. The use of this ’epoch’ helps to simplify the conversion functions, while the 32 bit value allows time to beproperly represented until Tue Feb 7 06:28:15 2136 UTC. The macros UNIX_OFFSET and NTP_OFFSET are definedto assist in converting to and from Unix and NTP time stamps.

Unlike desktop counterparts, it is impractical to implement or maintain the ’zoneinfo’ database. Therefore no attempt ismade to account for time zone, daylight saving, or leap seconds in past dates. All calculations are made according tothe currently configured time zone and daylight saving ’rule’.

In addition to C standard functions, re-entrant versions of ctime(), asctime(), gmtime() and localtime() are providedwhich, in addition to being re-entrant, have the property of claiming less permanent storage in RAM. An additional timeconversion, isotime() and its re-entrant version, uses far less storage than either ctime() or asctime().

Along with the usual smattering of utility functions, such as is_leap_year(), this library includes a set of functions relatedthe sun and moon, as well as sidereal time functions.


23.12.2.1 #define NTP_OFFSET 3155673600

Difference between the Y2K and the NTP epochs, in seconds. To convert a Y2K timestamp to NTP...

unsigned long ntp;time_t y2k;

y2k = time(NULL);ntp = y2k + NTP_OFFSET;

23.12.2.2 #define ONE_DAY 86400

One day, expressed in seconds

23.12.2.3 #define ONE_DEGREE 3600

Angular degree, expressed in arc seconds

23.12.2.4 #define ONE_HOUR 3600

One hour, expressed in seconds

23.12.2.5 #define UNIX_OFFSET 946684800

Difference between the Y2K and the UNIX epochs, in seconds. To convert a Y2K timestamp to UNIX...

long unix;time_t y2k;

y2k = time(NULL);unix = y2k + UNIX_OFFSET;


186 CONTENTS


23.12.3.1 typedef uint32_t time_t

time_t represents seconds elapsed from Midnight, Jan 1 2000 UTC (the Y2K ’epoch’). Its range allows this implemen-tation to represent time up to Tue Feb 7 06:28:15 2136 UTC.

23.12.4 Enumeration Type Documentation

23.12.4.1 enum _MONTHS_

Enumerated labels for the months.

23.12.4.2 enum _WEEK_DAYS_

Enumerated labels for the days of the week.


23.12.5.1 char∗ asctime ( const struct tm ∗ timeptr )

The asctime function converts the broken-down time of timeptr, into an ascii string in the form

Sun Mar 23 01:03:52 2013

23.12.5.2 void asctime_r ( const struct tm ∗ timeptr, char ∗ buf )

Re entrant version of asctime().

23.12.5.3 char∗ ctime ( const time_t ∗ timer )

The ctime function is equivalent to asctime(localtime(timer))

23.12.5.4 void ctime_r ( const time_t ∗ timer, char ∗ buf )

Re entrant version of ctime().

23.12.5.5 int32_t daylight_seconds ( const time_t ∗ timer )

Computes the amount of time the sun is above the horizon, at the location of the observer.

NOTE: At observer locations inside a polar circle, this value can be zero during the winter, and can exceed ONE_DAYduring the summer.

The returned value is in seconds.

23.12.5.6 int32_t difftime ( time_t time1, time_t time0 )

The difftime function returns the difference between two binary time stamps, time1 - time0.

23.12.5.7 int16_t equation_of_time ( const time_t ∗ timer )

Computes the difference between apparent solar time and mean solar time. The returned value is in seconds.


23.12 <time.h>: Time 187

23.12.5.8 uint32_t fatfs_time ( const struct tm ∗ timeptr )

Convert a Y2K time stamp into a FAT file system time stamp.

23.12.5.9 unsigned long gm_sidereal ( const time_t ∗ timer )

Returns Greenwich Mean Sidereal Time, as seconds into the sidereal day. The returned value will range from 0 through86399 seconds.

23.12.5.10 struct tm∗ gmtime ( const time_t ∗ timer )

The gmtime function converts the time stamp pointed to by timer into broken-down time, expressed as UTC.

23.12.5.11 void gmtime_r ( const time_t ∗ timer, struct tm ∗ timeptr )

Re entrant version of gmtime().

23.12.5.12 uint8_t is_leap_year ( int16_t year )

Return 1 if year is a leap year, zero if it is not.

23.12.5.13 struct week_date∗ iso_week_date ( int year, int yday )

Return a week_date structure with the ISO_8601 week based date corresponding to the given year and day of year.See http://en.wikipedia.org/wiki/ISO_week_date for more information.

23.12.5.14 void iso_week_date_r ( int year, int yday, struct week_date ∗ )

Re-entrant version of iso-week_date.

23.12.5.15 char∗ isotime ( const struct tm ∗ tmptr )

The isotime function constructs an ascii string in the form

2013-03-23 01:03:52

23.12.5.16 void isotime_r ( const struct tm ∗ , char ∗ )

Re entrant version of isotime()

23.12.5.17 unsigned long lm_sidereal ( const time_t ∗ timer )

Returns Local Mean Sidereal Time, as seconds into the sidereal day. The returned value will range from 0 through86399 seconds.

23.12.5.18 struct tm∗ localtime ( const time_t ∗ timer )

The localtime function converts the time stamp pointed to by timer into broken-down time, expressed as Local time.

23.12.5.19 void localtime_r ( const time_t ∗ timer, struct tm ∗ timeptr )

Re entrant version of localtime().

23.12.5.20 time_t mk_gmtime ( const struct tm ∗ timeptr )

This function ’compiles’ the elements of a broken-down time structure, returning a binary time stamp. The elements oftimeptr are interpreted as representing UTC.


http://en.wikipedia.org/wiki/ISO_week_date

188 CONTENTS

The original values of the tm_wday and tm_yday elements of the structure are ignored, and the original values of theother elements are not restricted to the ranges stated for struct tm.

Unlike mktime(), this function DOES NOT modify the elements of timeptr.

23.12.5.21 time_t mktime ( struct tm ∗ timeptr )

This function ’compiles’ the elements of a broken-down time structure, returning a binary time stamp. The elements oftimeptr are interpreted as representing Local Time.

The original values of the tm_wday and tm_yday elements of the structure are ignored, and the original values of theother elements are not restricted to the ranges stated for struct tm.

On successful completion, the values of all elements of timeptr are set to the appropriate range.

23.12.5.22 uint8_t month_length ( int16_t year, uint8_t month )

Return the length of month, given the year and month, where month is in the range 1 to 12.

23.12.5.23 int8_t moon_phase ( const time_t ∗ timer )

Returns an approximation to the phase of the moon. The sign of the returned value indicates a waning or waxing phase.The magnitude of the returned value indicates the percentage illumination.

23.12.5.24 void set_dst ( int(∗)(const time_t ∗, int32_t ∗) )

Specify the Daylight Saving function.

The Daylight Saving function should examine its parameters to determine whether Daylight Saving is in effect, and returna value appropriate for tm_isdst.

Working examples for the USA and the EU are available..

#include <util/eu_dst.h>

for the European Union, and

#include <util/usa_dst.h>

for the United States

If a Daylight Saving function is not specified, the system will ignore Daylight Saving.

23.12.5.25 void set_position ( int32_t latitude, int32_t longitude )

Set the geographic coordinates of the ’observer’, for use with several of the following functions. Parameters are passedas seconds of North Latitude, and seconds of East Longitude.

For New York City...

set_position( 40.7142 * ONE_DEGREE, -74.0064 * ONE_DEGREE);

23.12.5.26 void set_system_time ( time_t timestamp )

Initialize the system time. Examples are...

From a Clock / Calendar type RTC:

struct tm rtc_time;


23.12 <time.h>: Time 189

read_rtc(&rtc_time);rtc_time.tm_isdst = 0;set_system_time( mktime(&rtc_time) );

From a Network Time Protocol time stamp:

set_system_time(ntp_timestamp - NTP_OFFSET);

From a UNIX time stamp:

set_system_time(unix_timestamp - UNIX_OFFSET);

23.12.5.27 void set_zone ( int32_t )

Set the ’time zone’. The parameter is given in seconds East of the Prime Meridian. Example for New York City:

set_zone(-5 * ONE_HOUR);

If the time zone is not set, the time system will operate in UTC only.

23.12.5.28 double solar_declination ( const time_t ∗ timer )

Returns the declination of the sun in radians.

23.12.5.29 time_t solar_noon ( const time_t ∗ timer )

Computes the time of solar noon, at the location of the observer.

23.12.5.30 size_t strftime ( char ∗ s, size_t maxsize, const char ∗ format, const struct tm ∗ timeptr )

A complete description of strftime() is beyond the pale of this document. Refer to ISO/IEC document 9899 for details.

All conversions are made using the ’C Locale’, ignoring the E or O modifiers. Due to the lack of a time zone ’name’, the’Z’ conversion is also ignored.

23.12.5.31 time_t sun_rise ( const time_t ∗ timer )

Return the time of sunrise, at the location of the observer. See the note about daylight_seconds().

23.12.5.32 time_t sun_set ( const time_t ∗ timer )

Return the time of sunset, at the location of the observer. See the note about daylight_seconds().

23.12.5.33 void system_tick ( void )

Maintain the system time by calling this function at a rate of 1 Hertz.

It is anticipated that this function will typically be called from within an Interrupt Service Routine, (though that is notrequired). It therefore includes code which makes it simple to use from within a ’Naked’ ISR, avoiding the cost of savingand restoring all the cpu registers.

Such an ISR may resemble the following example...

ISR(RTC_OVF_vect, ISR_NAKED){

system_tick();reti();

}


190 CONTENTS

23.12.5.34 time_t time ( time_t ∗ timer )

The time function returns the systems current time stamp. If timer is not a null pointer, the return value is also assignedto the object it points to.

23.12.5.35 uint8_t week_of_month ( const struct tm ∗ timeptr, uint8_t start )

Return the calendar week of month, where the first week is considered to begin on the day of week specified by ’start’.The returned value may range from zero to 5.

23.12.5.36 uint8_t week_of_year ( const struct tm ∗ timeptr, uint8_t start )

Return the calendar week of year, where week 1 is considered to begin on the day of week specified by ’start’. Thereturned value may range from zero to 52.


23.13 <avr/boot.h>: Bootloader Support Utilities 191

23.13 <avr/boot.h>: Bootloader Support Utilities

Macros

• #define BOOTLOADER_SECTION __attribute__ ((section (".bootloader")))• #define boot_spm_interrupt_enable() (__SPM_REG |= (uint8_t)_BV(SPMIE))• #define boot_spm_interrupt_disable() (__SPM_REG &= (uint8_t)∼_BV(SPMIE))• #define boot_is_spm_interrupt() (__SPM_REG & (uint8_t)_BV(SPMIE))• #define boot_rww_busy() (__SPM_REG & (uint8_t)_BV(__COMMON_ASB))• #define boot_spm_busy() (__SPM_REG & (uint8_t)_BV(__SPM_ENABLE))• #define boot_spm_busy_wait() do{}while(boot_spm_busy())• #define GET_LOW_FUSE_BITS (0x0000)• #define GET_LOCK_BITS (0x0001)• #define GET_EXTENDED_FUSE_BITS (0x0002)• #define GET_HIGH_FUSE_BITS (0x0003)• #define boot_lock_fuse_bits_get(address)• #define boot_signature_byte_get(addr)• #define boot_page_fill(address, data) __boot_page_fill_normal(address, data)• #define boot_page_erase(address) __boot_page_erase_normal(address)• #define boot_page_write(address) __boot_page_write_normal(address)• #define boot_rww_enable() __boot_rww_enable()• #define boot_lock_bits_set(lock_bits) __boot_lock_bits_set(lock_bits)• #define boot_page_fill_safe(address, data)• #define boot_page_erase_safe(address)• #define boot_page_write_safe(address)• #define boot_rww_enable_safe()• #define boot_lock_bits_set_safe(lock_bits)


#include <avr/io.h>#include <avr/boot.h>

The macros in this module provide a C language interface to the bootloader support functionality of certain AVR pro-cessors. These macros are designed to work with all sizes of flash memory.

Global interrupts are not automatically disabled for these macros. It is left up to the programmer to do this. See the codeexample below. Also see the processor datasheet for caveats on having global interrupts enabled during writing of theFlash.

Note

Not all AVR processors provide bootloader support. See your processor datasheet to see if it provides bootloadersupport.

Todo From email with Marek: On smaller devices (all except ATmega64/128), __SPM_REG is in the I/O space, ac-cessible with the shorter "in" and "out" instructions - since the boot loader has a limited size, this could be animportant optimization.

API Usage Example

The following code shows typical usage of the boot API.


192 CONTENTS

#include <inttypes.h>#include <avr/interrupt.h>#include <avr/pgmspace.h>

void boot_program_page (uint32_t page, uint8_t *buf){

uint16_t i;uint8_t sreg;

// Disable interrupts.

sreg = SREG;cli();

eeprom_busy_wait ();

boot_page_erase (page);boot_spm_busy_wait (); // Wait until the memory is erased.

for (i=0; i<SPM_PAGESIZE; i+=2){

// Set up little-endian word.

uint16_t w = *buf++;w += (*buf++) << 8;

boot_page_fill (page + i, w);}

boot_page_write (page); // Store buffer in flash page.boot_spm_busy_wait(); // Wait until the memory is written.

// Reenable RWW-section again. We need this if we want to jump back// to the application after bootloading.

boot_rww_enable ();

// Re-enable interrupts (if they were ever enabled).

SREG = sreg;}


23.13.2.1 #define boot_is_spm_interrupt( ) (__SPM_REG & (uint8_t)_BV(SPMIE))

Check if the SPM interrupt is enabled.

23.13.2.2 #define boot_lock_bits_set( lock_bits ) __boot_lock_bits_set(lock_bits)

Set the bootloader lock bits.

Parameters

lock_bits A mask of which Boot Loader Lock Bits to set.

Note

In this context, a ’set bit’ will be written to a zero value. Note also that only BLBxx bits can be programmed by thiscommand.

For example, to disallow the SPM instruction from writing to the Boot Loader memory section of flash, you would usethis macro as such:

boot_lock_bits_set (_BV (BLB11));



Note

Like any lock bits, the Boot Loader Lock Bits, once set, cannot be cleared again except by a chip erase which willin turn also erase the boot loader itself.

23.13.2.3 #define boot_lock_bits_set_safe( lock_bits )

Value:

do { \boot_spm_busy_wait(); \eeprom_busy_wait(); \boot_lock_bits_set (lock_bits); \

} while (0)

Same as boot_lock_bits_set() except waits for eeprom and spm operations to complete before setting the lock bits.

23.13.2.4 #define boot_lock_fuse_bits_get( address )

Value:

(__extension__({ \uint8_t __result; \__asm__ __volatile__ \( \

"sts %1, %2\n\t" \"lpm %0, Z\n\t" \: "=r" (__result) \: "i" (_SFR_MEM_ADDR(__SPM_REG)), \"r" ((uint8_t)(__BOOT_LOCK_BITS_SET)), \"z" ((uint16_t)(address)) \

); \__result; \

}))

Read the lock or fuse bits at address.

Parameter address can be any of GET_LOW_FUSE_BITS, GET_LOCK_BITS, GET_EXTENDED_FUSE_BITS, orGET_HIGH_FUSE_BITS.

Note

The lock and fuse bits returned are the physical values, i.e. a bit returned as 0 means the corresponding fuse orlock bit is programmed.

23.13.2.5 #define boot_page_erase( address ) __boot_page_erase_normal(address)

Erase the flash page that contains address.

Note

address is a byte address in flash, not a word address.

23.13.2.6 #define boot_page_erase_safe( address )

Value:

do { \boot_spm_busy_wait(); \eeprom_busy_wait(); \boot_page_erase (address); \

} while (0)

Same as boot_page_erase() except it waits for eeprom and spm operations to complete before erasing the page.


194 CONTENTS

23.13.2.7 #define boot_page_fill( address, data ) __boot_page_fill_normal(address, data)

Fill the bootloader temporary page buffer for flash address with data word.

Note

The address is a byte address. The data is a word. The AVR writes data to the buffer a word at a time, butaddresses the buffer per byte! So, increment your address by 2 between calls, and send 2 data bytes in a wordformat! The LSB of the data is written to the lower address; the MSB of the data is written to the higher address.

23.13.2.8 #define boot_page_fill_safe( address, data )

Value:

do { \boot_spm_busy_wait(); \eeprom_busy_wait(); \boot_page_fill(address, data); \

} while (0)

Same as boot_page_fill() except it waits for eeprom and spm operations to complete before filling the page.

23.13.2.9 #define boot_page_write( address ) __boot_page_write_normal(address)

Write the bootloader temporary page buffer to flash page that contains address.

Note

address is a byte address in flash, not a word address.

23.13.2.10 #define boot_page_write_safe( address )

Value:

do { \boot_spm_busy_wait(); \eeprom_busy_wait(); \boot_page_write (address); \

} while (0)

Same as boot_page_write() except it waits for eeprom and spm operations to complete before writing the page.

23.13.2.11 #define boot_rww_busy( ) (__SPM_REG & (uint8_t)_BV(__COMMON_ASB))

Check if the RWW section is busy.

23.13.2.12 #define boot_rww_enable( ) __boot_rww_enable()

Enable the Read-While-Write memory section.

23.13.2.13 #define boot_rww_enable_safe( )

Value:

do { \boot_spm_busy_wait(); \eeprom_busy_wait(); \boot_rww_enable(); \

} while (0)

Same as boot_rww_enable() except waits for eeprom and spm operations to complete before enabling the RWW mame-ory.



23.13.2.14 #define boot_signature_byte_get( addr )

Value:

(__extension__({ \uint8_t __result; \__asm__ __volatile__ \( \

"sts %1, %2\n\t" \"lpm %0, Z" "\n\t" \: "=r" (__result) \: "i" (_SFR_MEM_ADDR(__SPM_REG)), \"r" ((uint8_t)(__BOOT_SIGROW_READ)), \"z" ((uint16_t)(addr)) \

); \__result; \

}))

Read the Signature Row byte at address. For some MCU types, this function can also retrieve the factory-storedoscillator calibration bytes.

Parameter address can be 0-0x1f as documented by the datasheet.

Note

The values are MCU type dependent.

23.13.2.15 #define boot_spm_busy( ) (__SPM_REG & (uint8_t)_BV(__SPM_ENABLE))

Check if the SPM instruction is busy.

23.13.2.16 #define boot_spm_busy_wait( ) do{}while(boot_spm_busy())

Wait while the SPM instruction is busy.

23.13.2.17 #define boot_spm_interrupt_disable( ) (__SPM_REG &= (uint8_t)∼_BV(SPMIE))

Disable the SPM interrupt.

23.13.2.18 #define boot_spm_interrupt_enable( ) (__SPM_REG |= (uint8_t)_BV(SPMIE))

Enable the SPM interrupt.

23.13.2.19 #define BOOTLOADER_SECTION __attribute__ ((section (".bootloader")))

Used to declare a function or variable to be placed into a new section called .bootloader. This section and its contentscan then be relocated to any address (such as the bootloader NRWW area) at link-time.

23.13.2.20 #define GET_EXTENDED_FUSE_BITS (0x0002)

address to read the extended fuse bits, using boot_lock_fuse_bits_get

23.13.2.21 #define GET_HIGH_FUSE_BITS (0x0003)

address to read the high fuse bits, using boot_lock_fuse_bits_get

23.13.2.22 #define GET_LOCK_BITS (0x0001)

address to read the lock bits, using boot_lock_fuse_bits_get


196 CONTENTS

23.13.2.23 #define GET_LOW_FUSE_BITS (0x0000)

address to read the low fuse bits, using boot_lock_fuse_bits_get


23.14 <avr/cpufunc.h>: Special AVR CPU functions 197

23.14 <avr/cpufunc.h>: Special AVR CPU functions

Macros

• #define _NOP()• #define _MemoryBarrier()


#include <avr/cpufunc.h>

This header file contains macros that access special functions of the AVR CPU which do not fit into any of the otherheader files.


23.14.2.1 #define _MemoryBarrier( )

Implement a read/write memory barrier. A memory barrier instructs the compiler to not cache any memory data inregisters beyond the barrier. This can sometimes be more effective than blocking certain optimizations by declaringsome object with a volatile qualifier.

See Problems with reordering code for things to be taken into account with respect to compiler optimizations.

23.14.2.2 #define _NOP( )

Execute a no operation (NOP) CPU instruction. This should not be used to implement delays, better use the func-tions from <util/delay_basic.h> or <util/delay.h> for this. For debugging purposes, a NOP can be useful to have aninstruction that is guaranteed to be not optimized away by the compiler, so it can always become a breakpoint in thedebugger.


198 CONTENTS

23.15 <avr/eeprom.h>: EEPROM handling

Macros

• #define EEMEM __attribute__((section(".eeprom")))• #define eeprom_is_ready()• #define eeprom_busy_wait() do {} while (!eeprom_is_ready())

Functions

• uint8_t eeprom_read_byte (const uint8_t ∗__p) __ATTR_PURE__• uint16_t eeprom_read_word (const uint16_t ∗__p) __ATTR_PURE__• uint32_t eeprom_read_dword (const uint32_t ∗__p) __ATTR_PURE__• float eeprom_read_float (const float ∗__p) __ATTR_PURE__• void eeprom_read_block (void ∗__dst, const void ∗__src, size_t __n)• void eeprom_write_byte (uint8_t ∗__p, uint8_t __value)• void eeprom_write_word (uint16_t ∗__p, uint16_t __value)• void eeprom_write_dword (uint32_t ∗__p, uint32_t __value)• void eeprom_write_float (float ∗__p, float __value)• void eeprom_write_block (const void ∗__src, void ∗__dst, size_t __n)• void eeprom_update_byte (uint8_t ∗__p, uint8_t __value)• void eeprom_update_word (uint16_t ∗__p, uint16_t __value)• void eeprom_update_dword (uint32_t ∗__p, uint32_t __value)• void eeprom_update_float (float ∗__p, float __value)• void eeprom_update_block (const void ∗__src, void ∗__dst, size_t __n)

IAR C compatibility defines

• #define _EEPUT(addr, val) eeprom_write_byte ((uint8_t ∗)(addr), (uint8_t)(val))• #define __EEPUT(addr, val) eeprom_write_byte ((uint8_t ∗)(addr), (uint8_t)(val))• #define _EEGET(var, addr) (var) = eeprom_read_byte ((const uint8_t ∗)(addr))• #define __EEGET(var, addr) (var) = eeprom_read_byte ((const uint8_t ∗)(addr))


#include <avr/eeprom.h>

This header file declares the interface to some simple library routines suitable for handling the data EEPROM con-tained in the AVR microcontrollers. The implementation uses a simple polled mode interface. Applications that requireinterrupt-controlled EEPROM access to ensure that no time will be wasted in spinloops will have to deploy their ownimplementation.

Notes:

• In addition to the write functions there is a set of update ones. This functions read each byte first and skip theburning if the old value is the same with new. The scaning direction is from high address to low, to obtain quickreturn in common cases.


23.15 <avr/eeprom.h>: EEPROM handling 199

• All of the read/write functions first make sure the EEPROM is ready to be accessed. Since this may cause longdelays if a write operation is still pending, time-critical applications should first poll the EEPROM e. g. usingeeprom_is_ready() before attempting any actual I/O. But this functions are not wait until SELFPRGEN in SPM←↩CSR becomes zero. Do this manually, if your softwate contains the Flash burning.

• As these functions modify IO registers, they are known to be non-reentrant. If any of these functions are used fromboth, standard and interrupt context, the applications must ensure proper protection (e.g. by disabling interruptsbefore accessing them).

• All write functions force erase_and_write programming mode.

• For Xmega the EEPROM start address is 0, like other architectures. The reading functions add the 0x2000 valueto use EEPROM mapping into data space.


23.15.2.1 #define __EEGET( var, addr ) (var) = eeprom_read_byte ((const uint8_t ∗)(addr))

Read a byte from EEPROM. Compatibility define for IAR C.

23.15.2.2 #define __EEPUT( addr, val ) eeprom_write_byte ((uint8_t ∗)(addr), (uint8_t)(val))

Write a byte to EEPROM. Compatibility define for IAR C.

23.15.2.3 #define _EEGET( var, addr ) (var) = eeprom_read_byte ((const uint8_t ∗)(addr))

Read a byte from EEPROM. Compatibility define for IAR C.

23.15.2.4 #define _EEPUT( addr, val ) eeprom_write_byte ((uint8_t ∗)(addr), (uint8_t)(val))

Write a byte to EEPROM. Compatibility define for IAR C.

23.15.2.5 #define EEMEM __attribute__((section(".eeprom")))

Attribute expression causing a variable to be allocated within the .eeprom section.

23.15.2.6 #define eeprom_busy_wait( ) do {} while (!eeprom_is_ready())

Loops until the eeprom is no longer busy.

Returns

Nothing.

23.15.2.7 #define eeprom_is_ready( )

Returns

1 if EEPROM is ready for a new read/write operation, 0 if not.


23.15.3.1 void eeprom_read_block ( void ∗ __dst, const void ∗ __src, size_t __n )

Read a block of __n bytes from EEPROM address __src to SRAM __dst.


200 CONTENTS

23.15.3.2 uint8_t eeprom_read_byte ( const uint8_t ∗ __p )

Read one byte from EEPROM address __p.

23.15.3.3 uint32_t eeprom_read_dword ( const uint32_t ∗ __p )

Read one 32-bit double word (little endian) from EEPROM address __p.

23.15.3.4 float eeprom_read_float ( const float ∗ __p )

Read one float value (little endian) from EEPROM address __p.

23.15.3.5 uint16_t eeprom_read_word ( const uint16_t ∗ __p )

Read one 16-bit word (little endian) from EEPROM address __p.

23.15.3.6 void eeprom_update_block ( const void ∗ __src, void ∗ __dst, size_t __n )

Update a block of __n bytes to EEPROM address __dst from __src.

Note

The argument order is mismatch with common functions like strcpy().

23.15.3.7 void eeprom_update_byte ( uint8_t ∗ __p, uint8_t __value )

Update a byte __value to EEPROM address __p.

23.15.3.8 void eeprom_update_dword ( uint32_t ∗ __p, uint32_t __value )

Update a 32-bit double word __value to EEPROM address __p.

23.15.3.9 void eeprom_update_float ( float ∗ __p, float __value )

Update a float __value to EEPROM address __p.

23.15.3.10 void eeprom_update_word ( uint16_t ∗ __p, uint16_t __value )

Update a word __value to EEPROM address __p.

23.15.3.11 void eeprom_write_block ( const void ∗ __src, void ∗ __dst, size_t __n )

Write a block of __n bytes to EEPROM address __dst from __src.

Note

The argument order is mismatch with common functions like strcpy().

23.15.3.12 void eeprom_write_byte ( uint8_t ∗ __p, uint8_t __value )

Write a byte __value to EEPROM address __p.

23.15.3.13 void eeprom_write_dword ( uint32_t ∗ __p, uint32_t __value )

Write a 32-bit double word __value to EEPROM address __p.


23.15 <avr/eeprom.h>: EEPROM handling 201

23.15.3.14 void eeprom_write_float ( float ∗ __p, float __value )

Write a float __value to EEPROM address __p.

23.15.3.15 void eeprom_write_word ( uint16_t ∗ __p, uint16_t __value )

Write a word __value to EEPROM address __p.


202 CONTENTS

23.16 <avr/fuse.h>: Fuse Support

Introduction

The Fuse API allows a user to specify the fuse settings for the specific AVR device they are compiling for. These fusesettings will be placed in a special section in the ELF output file, after linking.

Programming tools can take advantage of the fuse information embedded in the ELF file, by extracting this informationand determining if the fuses need to be programmed before programming the Flash and EEPROM memories. This alsoallows a single ELF file to contain all the information needed to program an AVR.

To use the Fuse API, include the <avr/io.h> header file, which in turn automatically includes the individual I/O headerfile and the <avr/fuse.h> file. These other two files provides everything necessary to set the AVR fuses.

Fuse API

Each I/O header file must define the FUSE_MEMORY_SIZE macro which is defined to the number of fuse bytes thatexist in the AVR device.

A new type, __fuse_t, is defined as a structure. The number of fields in this structure are determined by the number offuse bytes in the FUSE_MEMORY_SIZE macro.

If FUSE_MEMORY_SIZE == 1, there is only a single field: byte, of type unsigned char.

If FUSE_MEMORY_SIZE == 2, there are two fields: low, and high, of type unsigned char.

If FUSE_MEMORY_SIZE == 3, there are three fields: low, high, and extended, of type unsigned char.

If FUSE_MEMORY_SIZE > 3, there is a single field: byte, which is an array of unsigned char with the size of the arraybeing FUSE_MEMORY_SIZE.

A convenience macro, FUSEMEM, is defined as a GCC attribute for a custom-named section of ".fuse".

A convenience macro, FUSES, is defined that declares a variable, __fuse, of type __fuse_t with the attribute defined byFUSEMEM. This variable allows the end user to easily set the fuse data.

Note

If a device-specific I/O header file has previously defined FUSEMEM, then FUSEMEM is not redefined. If a device-specific I/O header file has previously defined FUSES, then FUSES is not redefined.

Each AVR device I/O header file has a set of defined macros which specify the actual fuse bits available on that device.The AVR fuses have inverted values, logical 1 for an unprogrammed (disabled) bit and logical 0 for a programmed(enabled) bit. The defined macros for each individual fuse bit represent this in their definition by a bit-wise inversion ofa mask. For example, the FUSE_EESAVE fuse in the ATmega128 is defined as:

#define FUSE_EESAVE ~_BV(3)

Note

The _BV macro creates a bit mask from a bit number. It is then inverted to represent logical values for a fusememory byte.

To combine the fuse bits macros together to represent a whole fuse byte, use the bitwise AND operator, like so:

(FUSE_BOOTSZ0 & FUSE_BOOTSZ1 & FUSE_EESAVE & FUSE_SPIEN & FUSE_JTAGEN)


23.16 <avr/fuse.h>: Fuse Support 203

Each device I/O header file also defines macros that provide default values for each fuse byte that is available. LFUS←↩E_DEFAULT is defined for a Low Fuse byte. HFUSE_DEFAULT is defined for a High Fuse byte. EFUSE_DEFAULT isdefined for an Extended Fuse byte.

If FUSE_MEMORY_SIZE > 3, then the I/O header file defines macros that provide default values for each fuse byte likeso: FUSE0_DEFAULT FUSE1_DEFAULT FUSE2_DEFAULT FUSE3_DEFAULT FUSE4_DEFAULT ....

API Usage Example

Putting all of this together is easy. Using C99’s designated initializers:

#include <avr/io.h>

FUSES ={

.low = LFUSE_DEFAULT,

.high = (FUSE_BOOTSZ0 & FUSE_BOOTSZ1 & FUSE_EESAVE & FUSE_SPIEN & FUSE_JTAGEN),

.extended = EFUSE_DEFAULT,};

int main(void){

return 0;}

Or, using the variable directly instead of the FUSES macro,

#include <avr/io.h>

__fuse_t __fuse __attribute__((section (".fuse"))) ={

.low = LFUSE_DEFAULT,

.high = (FUSE_BOOTSZ0 & FUSE_BOOTSZ1 & FUSE_EESAVE & FUSE_SPIEN & FUSE_JTAGEN),

.extended = EFUSE_DEFAULT,};

int main(void){

return 0;}

If you are compiling in C++, you cannot use the designated intializers so you must do:

#include <avr/io.h>

FUSES ={

LFUSE_DEFAULT, // .low(FUSE_BOOTSZ0 & FUSE_BOOTSZ1 & FUSE_EESAVE & FUSE_SPIEN & FUSE_JTAGEN), // .highEFUSE_DEFAULT, // .extended

};

int main(void){

return 0;}

However there are a number of caveats that you need to be aware of to use this API properly.

Be sure to include <avr/io.h> to get all of the definitions for the API. The FUSES macro defines a global variable tostore the fuse data. This variable is assigned to its own linker section. Assign the desired fuse values immediately inthe variable initialization.

The .fuse section in the ELF file will get its values from the initial variable assignment ONLY. This means that you canNOT assign values to this variable in functions and the new values will not be put into the ELF .fuse section.


204 CONTENTS

The global variable is declared in the FUSES macro has two leading underscores, which means that it is reserved forthe "implementation", meaning the library, so it will not conflict with a user-named variable.

You must initialize ALL fields in the __fuse_t structure. This is because the fuse bits in all bytes default to a logical1, meaning unprogrammed. Normal uninitialized data defaults to all locgial zeros. So it is vital that all fuse bytes areinitialized, even with default data. If they are not, then the fuse bits may not programmed to the desired settings.

Be sure to have the -mmcu=device flag in your compile command line and your linker command line to have the correctdevice selected and to have the correct I/O header file included when you include <avr/io.h>.

You can print out the contents of the .fuse section in the ELF file by using this command line:

avr-objdump -s -j .fuse <ELF file>

The section contents shows the address on the left, then the data going from lower address to a higher address, left toright.


23.17 <avr/interrupt.h>: Interrupts 205

23.17 <avr/interrupt.h>: Interrupts

Global manipulation of the interrupt flag

The global interrupt flag is maintained in the I bit of the status register (SREG).

Handling interrupts frequently requires attention regarding atomic access to objects that could be altered by code runningwithin an interrupt context, see <util/atomic.h>.

Frequently, interrupts are being disabled for periods of time in order to perform certain operations without being dis-turbed; see Problems with reordering code for things to be taken into account with respect to compiler optimizations.

• #define sei()• #define cli()

Macros for writing interrupt handler functions

• #define ISR(vector, attributes)• #define SIGNAL(vector)• #define EMPTY_INTERRUPT(vector)• #define ISR_ALIAS(vector, target_vector)• #define reti()• #define BADISR_vect

ISR attributes

• #define ISR_BLOCK• #define ISR_NOBLOCK• #define ISR_NAKED• #define ISR_ALIASOF(target_vector)


Note

This discussion of interrupts was originally taken from Rich Neswold’s document. See Acknowledgments.

Introduction to avr-libc’s interrupt handling

It’s nearly impossible to find compilers that agree on how to handle interrupt code. Since the C language tries to stayaway from machine dependent details, each compiler writer is forced to design their method of support.

In the AVR-GCC environment, the vector table is predefined to point to interrupt routines with predetermined names.By using the appropriate name, your routine will be called when the corresponding interrupt occurs. The device libraryprovides a set of default interrupt routines, which will get used if you don’t define your own.

Patching into the vector table is only one part of the problem. The compiler uses, by convention, a set of registers whenit’s normally executing compiler-generated code. It’s important that these registers, as well as the status register, getsaved and restored. The extra code needed to do this is enabled by tagging the interrupt function with __attribute←↩__((signal)).

These details seem to make interrupt routines a little messy, but all these details are handled by the Interrupt API. Aninterrupt routine is defined with ISR(). This macro register and mark the routine as an interrupt handler for the specifiedperipheral. The following is an example definition of a handler for the ADC interrupt.


206 CONTENTS


ISR(ADC_vect){

// user code here}

Refer to the chapter explaining assembler programming for an explanation about interrupt routines written solely inassembler language.

Catch-all interrupt vector

If an unexpected interrupt occurs (interrupt is enabled and no handler is installed, which usually indicates a bug), thenthe default action is to reset the device by jumping to the reset vector. You can override this by supplying a functionnamed BADISR_vect which should be defined with ISR() as such. (The name BADISR_vect is actually an alias for__vector_default. The latter must be used inside assembly code in case <avr/interrupt.h> is not included.)


ISR(BADISR_vect){

// user code here}

Nested interrupts

The AVR hardware clears the global interrupt flag in SREG before entering an interrupt vector. Thus, normally interruptswill remain disabled inside the handler until the handler exits, where the RETI instruction (that is emitted by the compileras part of the normal function epilogue for an interrupt handler) will eventually re-enable further interrupts. For thatreason, interrupt handlers normally do not nest. For most interrupt handlers, this is the desired behaviour, for someit is even required in order to prevent infinitely recursive interrupts (like UART interrupts, or level-triggered externalinterrupts). In rare circumstances though it might be desired to re-enable the global interrupt flag as early as possiblein the interrupt handler, in order to not defer any other interrupt more than absolutely needed. This could be doneusing an sei() instruction right at the beginning of the interrupt handler, but this still leaves few instructions inside thecompiler-generated function prologue to run with global interrupts disabled. The compiler can be instructed to insert anSEI instruction right at the beginning of an interrupt handler by declaring the handler the following way:

ISR(XXX_vect, ISR_NOBLOCK){

...}

where XXX_vect is the name of a valid interrupt vector for the MCU type in question, as explained below.

Two vectors sharing the same code

In some circumstances, the actions to be taken upon two different interrupts might be completely identical so a singleimplementation for the ISR would suffice. For example, pin-change interrupts arriving from two different ports couldlogically signal an event that is independent from the actual port (and thus interrupt vector) where it happened. Sharinginterrupt vector code can be accomplished using the ISR_ALIASOF() attribute to the ISR macro:

ISR(PCINT0_vect){

...// Code to handle the event.

}

ISR(PCINT1_vect, ISR_ALIASOF(PCINT0_vect));



Note

There is no body to the aliased ISR.

Note that the ISR_ALIASOF() feature requires GCC 4.2 or above (or a patched version of GCC 4.1.x). See the doc-umentation of the ISR_ALIAS() macro for an implementation which is less elegant but could be applied to all compilerversions.

Empty interrupt service routines

In rare circumstances, in interrupt vector does not need any code to be implemented at all. The vector must be declaredanyway, so when the interrupt triggers it won’t execute the BADISR_vect code (which by default restarts the application).

This could for example be the case for interrupts that are solely enabled for the purpose of getting the controller out ofsleep_mode().

A handler for such an interrupt vector can be declared using the EMPTY_INTERRUPT() macro:

EMPTY_INTERRUPT(ADC_vect);

Note

There is no body to this macro.

Manually defined ISRs

In some circumstances, the compiler-generated prologue and epilogue of the ISR might not be optimal for the job, anda manually defined ISR could be considered particularly to speedup the interrupt handling.

One solution to this could be to implement the entire ISR as manual assembly code in a separate (assembly) file. SeeCombining C and assembly source files for an example of how to implement it that way.

Another solution is to still implement the ISR in C language but take over the compiler’s job of generating the prologueand epilogue. This can be done using the ISR_NAKED attribute to the ISR() macro. Note that the compiler does notgenerate anything as prologue or epilogue, so the final reti() must be provided by the actual implementation. SREGmust be manually saved if the ISR code modifies it, and the compiler-implied assumption of zero_reg always being0 could be wrong (e. g. when interrupting right after of a MUL instruction).

ISR(TIMER1_OVF_vect, ISR_NAKED){

PORTB |= _BV(0); // results in SBI which does not affect SREGreti();

}

Choosing the vector: Interrupt vector names

The interrupt is chosen by supplying one of the symbols in following table.

There are currently two different styles present for naming the vectors. One form uses names starting with SIG_←↩, followed by a relatively verbose but arbitrarily chosen name describing the interrupt vector. This has been the onlyavailable style in avr-libc up to version 1.2.x.

Starting with avr-libc version 1.4.0, a second style of interrupt vector names has been added, where a short phrase forthe vector description is followed by _vect. The short phrase matches the vector name as described in the datasheetof the respective device (and in Atmel’s XML files), with spaces replaced by an underscore and other non-alphanumericcharacters dropped. Using the suffix _vect is intented to improve portability to other C compilers available for the AVRthat use a similar naming convention.

The historical naming style might become deprecated in a future release, so it is not recommended for new projects.


208 CONTENTS

Note

The ISR() macro cannot really spell-check the argument passed to them. Thus, by misspelling one of the namesbelow in a call to ISR(), a function will be created that, while possibly being usable as an interrupt function, isnot actually wired into the interrupt vector table. The compiler will generate a warning if it detects a suspiciouslylooking name of a ISR() function (i.e. one that after macro replacement does not start with "__vector_").

Vector name Old vectorname

Description Applicable for device

ADC_vect SIG_ADC ADC ConversionComplete

AT90S2333, AT90S4433, AT90S4434, A←↩T90S8535, AT90PWM216, AT90PWM2B,AT90PWM316, AT90PWM3B, AT90PWM3,AT90PWM2, AT90PWM1, AT90CAN128,AT90CAN32, AT90CAN64, ATmega103,ATmega128, ATmega1284P, ATmega16,ATmega163, ATmega165, ATmega165P,ATmega168P, ATmega169, ATmega169P,ATmega32, ATmega323, ATmega325, A←↩Tmega3250, ATmega3250P, ATmega328P,ATmega329, ATmega3290, ATmega3290←↩P, ATmega48P, ATmega64, ATmega645,ATmega6450, ATmega649, ATmega6490,ATmega8, ATmega8535, ATmega88P, A←↩Tmega168, ATmega48, ATmega88, A←↩Tmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561, ATmega324←↩P, ATmega164P, ATmega644P, ATmega644,ATtiny13, ATtiny15, ATtiny26, ATtiny43U,ATtiny48, ATtiny24, ATtiny44, ATtiny84, A←↩Ttiny45, ATtiny25, ATtiny85, ATtiny261, A←↩Ttiny461, ATtiny861, AT90USB1287, A←↩T90USB1286, AT90USB647, AT90USB646

ANALOG_C←↩OMP_0_vect

SIG_COMP←↩ARATOR0

Analog Compara-tor 0

AT90PWM3, AT90PWM2, AT90PWM1









ANALOG_C←↩OMP_vect

SIG_COMP←↩ARATOR

Analog Compara-tor

AT90CAN128, AT90CAN32, AT90C←↩AN64, ATmega103, ATmega128, A←↩Tmega1284P, ATmega165, ATmega165P,ATmega168P, ATmega169, ATmega169P,ATmega325, ATmega3250, ATmega3250P,ATmega328P, ATmega329, ATmega3290,ATmega3290P, ATmega48P, ATmega64,ATmega645, ATmega6450, ATmega649,ATmega6490, ATmega88P, ATmega168,ATmega48, ATmega88, ATmega640, A←↩Tmega1280, ATmega1281, ATmega2560,ATmega2561, ATmega324P, ATmega164P,ATmega644P, ATmega644, AT90USB162,AT90USB82, AT90USB1287, AT90US←↩B1286, AT90USB647, AT90USB646

ANA_COMP←↩_vect

SIG_COMP←↩ARATOR

Analog Compara-tor

AT90S1200, AT90S2313, AT90S2333, A←↩T90S4414, AT90S4433, AT90S4434, A←↩T90S8515, AT90S8535, ATmega16, A←↩Tmega161, ATmega162, ATmega163, A←↩Tmega32, ATmega323, ATmega8, A←↩Tmega8515, ATmega8535, ATtiny11, A←↩Ttiny12, ATtiny13, ATtiny15, ATtiny2313,ATtiny26, ATtiny28, ATtiny43U, ATtiny48,ATtiny24, ATtiny44, ATtiny84, ATtiny45, A←↩Ttiny25, ATtiny85, ATtiny261, ATtiny461,ATtiny861

CANIT_vect SIG_CAN_I←↩NTERRUPT1

CAN TransferComplete or Error

AT90CAN128, AT90CAN32, AT90CAN64



EEPROM_R←↩EADY_vect

SIG_EEPR←↩OM_READY,SIG_EE_RE←↩ADY

ATtiny2313

EE_RDY_vect SIG_EEPR←↩OM_READY

EEPROM Ready AT90S2333, AT90S4433, AT90S4434, A←↩T90S8535, ATmega16, ATmega161, A←↩Tmega162, ATmega163, ATmega32, A←↩Tmega323, ATmega8, ATmega8515, A←↩Tmega8535, ATtiny12, ATtiny13, ATtiny15,ATtiny26, ATtiny43U, ATtiny48, ATtiny24,ATtiny44, ATtiny84, ATtiny45, ATtiny25, A←↩Ttiny85, ATtiny261, ATtiny461, ATtiny861

EE_READY←↩_vect

SIG_EEPR←↩OM_READY

EEPROM Ready AT90PWM3, AT90PWM2, AT90PWM1,AT90CAN128, AT90CAN32, AT90C←↩AN64, ATmega103, ATmega128, A←↩Tmega1284P, ATmega165, ATmega165P,ATmega168P, ATmega169, ATmega169P,ATmega325, ATmega3250, ATmega3250P,ATmega328P, ATmega329, ATmega3290,ATmega3290P, ATmega32HVB, A←↩Tmega406, ATmega48P, ATmega64,ATmega645, ATmega6450, ATmega649,ATmega6490, ATmega88P, ATmega168,ATmega48, ATmega88, ATmega640, A←↩Tmega1280, ATmega1281, ATmega2560,ATmega2561, ATmega324P, ATmega164P,ATmega644P, ATmega644, ATmega16HVA,AT90USB162, AT90USB82, AT90US←↩B1287, AT90USB1286, AT90USB647,AT90USB646

EXT_INT0_←↩vect

SIG_INTER←↩RUPT0

External InterruptRequest 0

ATtiny24, ATtiny44, ATtiny84

INT0_vect SIG_INTER←↩RUPT0

External Interrupt0

AT90S1200, AT90S2313, AT90S2323, A←↩T90S2333, AT90S2343, AT90S4414, A←↩T90S4433, AT90S4434, AT90S8515, A←↩T90S8535, AT90PWM216, AT90PWM2←↩B, AT90PWM316, AT90PWM3B, AT90P←↩WM3, AT90PWM2, AT90PWM1, AT90←↩CAN128, AT90CAN32, AT90CAN64, A←↩Tmega103, ATmega128, ATmega1284←↩P, ATmega16, ATmega161, ATmega162,ATmega163, ATmega165, ATmega165P,ATmega168P, ATmega169, ATmega169P,ATmega32, ATmega323, ATmega325, A←↩Tmega3250, ATmega3250P, ATmega328P,ATmega329, ATmega3290, ATmega3290P,ATmega32HVB, ATmega406, ATmega48←↩P, ATmega64, ATmega645, ATmega6450,ATmega649, ATmega6490, ATmega8, A←↩Tmega8515, ATmega8535, ATmega88←↩P, ATmega168, ATmega48, ATmega88,ATmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561, ATmega324←↩P, ATmega164P, ATmega644P, ATmega644,ATmega16HVA, ATtiny11, ATtiny12, A←↩Ttiny13, ATtiny15, ATtiny22, ATtiny2313,ATtiny26, ATtiny28, ATtiny43U, ATtiny48,ATtiny45, ATtiny25, ATtiny85, ATtiny261,ATtiny461, ATtiny861, AT90USB162, A←↩T90USB82, AT90USB1287, AT90USB1286,AT90USB647, AT90USB646


210 CONTENTS



AT90S2313, AT90S2333, AT90S4414, A←↩T90S4433, AT90S4434, AT90S8515, A←↩T90S8535, AT90PWM216, AT90PWM2←↩B, AT90PWM316, AT90PWM3B, AT90P←↩WM3, AT90PWM2, AT90PWM1, AT90←↩CAN128, AT90CAN32, AT90CAN64, A←↩Tmega103, ATmega128, ATmega1284←↩P, ATmega16, ATmega161, ATmega162,ATmega163, ATmega168P, ATmega32, A←↩Tmega323, ATmega328P, ATmega32HVB,ATmega406, ATmega48P, ATmega64, A←↩Tmega8, ATmega8515, ATmega8535, A←↩Tmega88P, ATmega168, ATmega48, A←↩Tmega88, ATmega640, ATmega1280, A←↩Tmega1281, ATmega2560, ATmega2561,ATmega324P, ATmega164P, ATmega644←↩P, ATmega644, ATmega16HVA, ATtiny2313,ATtiny28, ATtiny48, ATtiny261, ATtiny461,ATtiny861, AT90USB162, AT90USB82, A←↩T90USB1287, AT90USB1286, AT90US←↩B647, AT90USB646



AT90PWM3, AT90PWM2, AT90PWM1, A←↩T90CAN128, AT90CAN32, AT90CAN64,ATmega103, ATmega128, ATmega1284←↩P, ATmega16, ATmega161, ATmega162,ATmega32, ATmega323, ATmega32HV←↩B, ATmega406, ATmega64, ATmega8515,ATmega8535, ATmega640, ATmega1280,ATmega1281, ATmega2560, ATmega2561,ATmega324P, ATmega164P, ATmega644←↩P, ATmega644, ATmega16HVA, AT90US←↩B162, AT90USB82, AT90USB1287, AT90←↩USB1286, AT90USB647, AT90USB646



AT90PWM3, AT90PWM2, AT90PWM1, A←↩T90CAN128, AT90CAN32, AT90CAN64,ATmega103, ATmega128, ATmega32HV←↩B, ATmega406, ATmega64, ATmega640,ATmega1280, ATmega1281, ATmega2560,ATmega2561, AT90USB162, AT90USB82,AT90USB1287, AT90USB1286, AT90US←↩B647, AT90USB646



AT90CAN128, AT90CAN32, AT90CAN64,ATmega103, ATmega128, ATmega64, A←↩Tmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561, AT90USB162,AT90USB82, AT90USB1287, AT90US←↩B1286, AT90USB647, AT90USB646










IO_PINS_vect SIG_PIN,SIG_PIN_C←↩HANGE


ATtiny11, ATtiny12, ATtiny15, ATtiny26



LCD_vect SIG_LCD LCD Start ofFrame

ATmega169, ATmega169P, ATmega329,ATmega3290, ATmega3290P, ATmega649,ATmega6490

LOWLEVEL←↩_IO_PINS_←↩vect

SIG_PIN Low-level Inputon Port B

ATtiny28

OVRIT_vect SIG_CAN_←↩OVERFLOW1

CAN Timer Over-run

AT90CAN128, AT90CAN32, AT90CAN64

PCINT0_vect SIG_PIN_C←↩HANGE0

Pin Change Inter-rupt Request 0

ATmega162, ATmega165, ATmega165P,ATmega168P, ATmega169, ATmega169P,ATmega325, ATmega3250, ATmega3250P,ATmega328P, ATmega329, ATmega3290,ATmega3290P, ATmega32HVB, A←↩Tmega406, ATmega48P, ATmega645,ATmega6450, ATmega649, ATmega6490,ATmega88P, ATmega168, ATmega48,ATmega88, ATmega640, ATmega1280,ATmega1281, ATmega2560, ATmega2561,ATmega324P, ATmega164P, ATmega644P,ATmega644, ATtiny13, ATtiny43U, ATtiny48,ATtiny24, ATtiny44, ATtiny84, ATtiny45,ATtiny25, ATtiny85, AT90USB162, AT90←↩USB82, AT90USB1287, AT90USB1286,AT90USB647, AT90USB646



ATmega162, ATmega165, ATmega165P,ATmega168P, ATmega169, ATmega169P,ATmega325, ATmega3250, ATmega3250P,ATmega328P, ATmega329, ATmega3290,ATmega3290P, ATmega32HVB, A←↩Tmega406, ATmega48P, ATmega645,ATmega6450, ATmega649, ATmega6490,ATmega88P, ATmega168, ATmega48,ATmega88, ATmega640, ATmega1280,ATmega1281, ATmega2560, ATmega2561,ATmega324P, ATmega164P, ATmega644P,ATmega644, ATtiny43U, ATtiny48, A←↩Ttiny24, ATtiny44, ATtiny84, AT90USB162,AT90USB82



ATmega3250, ATmega3250P, A←↩Tmega328P, ATmega3290, ATmega3290P,ATmega48P, ATmega6450, ATmega6490,ATmega88P, ATmega168, ATmega48,ATmega88, ATmega640, ATmega1280,ATmega1281, ATmega2560, ATmega2561,ATmega324P, ATmega164P, ATmega644P,ATmega644, ATtiny48



ATmega3250, ATmega3250P, A←↩Tmega3290, ATmega3290P, ATmega6450,ATmega6490, ATmega324P, ATmega164P,ATmega644P, ATmega644, ATtiny48

PCINT_vect SIG_PIN←↩_CHANGE,SIG_PCINT

ATtiny2313, ATtiny261, ATtiny461, A←↩Ttiny861

PSC0_CAP←↩T_vect

SIG_PSC0_←↩CAPTURE

PSC0 CaptureEvent


PSC0_EC_←↩vect

SIG_PSC0_←↩END_CYCLE

PSC0 End Cycle AT90PWM3, AT90PWM2, AT90PWM1



PSC1 CaptureEvent


PSC1_EC_←↩vect





PSC2 CaptureEvent


PSC2_EC_←↩vect




212 CONTENTS

SPI_STC_vect SIG_SPI Serial TransferComplete

AT90S2333, AT90S4414, AT90S4433,AT90S4434, AT90S8515, AT90S8535,AT90PWM216, AT90PWM2B, AT90←↩PWM316, AT90PWM3B, AT90PWM3,AT90PWM2, AT90PWM1, AT90CAN128,AT90CAN32, AT90CAN64, ATmega103,ATmega128, ATmega1284P, ATmega16,ATmega161, ATmega162, ATmega163,ATmega165, ATmega165P, ATmega168P,ATmega169, ATmega169P, ATmega32,ATmega323, ATmega325, ATmega3250,ATmega3250P, ATmega328P, ATmega329,ATmega3290, ATmega3290P, ATmega32←↩HVB, ATmega48P, ATmega64, ATmega645,ATmega6450, ATmega649, ATmega6490,ATmega8, ATmega8515, ATmega8535,ATmega88P, ATmega168, ATmega48,ATmega88, ATmega640, ATmega1280,ATmega1281, ATmega2560, ATmega2561,ATmega324P, ATmega164P, ATmega644P,ATmega644, ATmega16HVA, ATtiny48,AT90USB162, AT90USB82, AT90US←↩B1287, AT90USB1286, AT90USB647,AT90USB646

SPM_RDY_←↩vect

SIG_SPM_←↩READY

Store ProgramMemory Ready

ATmega16, ATmega162, ATmega32, A←↩Tmega323, ATmega8, ATmega8515, A←↩Tmega8535

SPM_READ←↩Y_vect

SIG_SPM_←↩READY

Store ProgramMemory Read

AT90PWM3, AT90PWM2, AT90PWM1, A←↩T90CAN128, AT90CAN32, AT90CAN64,ATmega128, ATmega1284P, ATmega165,ATmega165P, ATmega168P, ATmega169,ATmega169P, ATmega325, ATmega3250,ATmega3250P, ATmega328P, ATmega329,ATmega3290, ATmega3290P, ATmega406,ATmega48P, ATmega64, ATmega645, A←↩Tmega6450, ATmega649, ATmega6490,ATmega88P, ATmega168, ATmega48, A←↩Tmega88, ATmega640, ATmega1280, A←↩Tmega1281, ATmega2560, ATmega2561,ATmega324P, ATmega164P, ATmega644←↩P, ATmega644, AT90USB162, AT90USB82,AT90USB1287, AT90USB1286, AT90US←↩B647, AT90USB646

TIM0_COM←↩PA_vect

SIG_OUTP←↩UT_COMPA←↩RE0A

Timer/CounterCompare MatchA

ATtiny13, ATtiny43U, ATtiny24, ATtiny44,ATtiny84, ATtiny45, ATtiny25, ATtiny85

TIM0_COM←↩PB_vect

SIG_OUTP←↩UT_COMPA←↩RE0B

Timer/CounterCompare MatchB


TIM0_OVF_←↩vect

SIG_OVER←↩FLOW0

Timer/Counter0Overflow


TIM1_CAPT←↩_vect

SIG_INPUT←↩_CAPTURE1

Timer/Counter1Capture Event


TIM1_COM←↩PA_vect


Timer/Counter1Compare MatchA

ATtiny24, ATtiny44, ATtiny84, ATtiny45, A←↩Ttiny25, ATtiny85

TIM1_COM←↩PB_vect


Timer/Counter1Compare MatchB


TIM1_OVF_←↩vect

SIG_OVER←↩FLOW1



TIMER0_CA←↩PT_vect


ADC ConversionComplete




TIMER0_C←↩OMPA_vect


TimerCounter0Compare MatchA

ATmega168, ATmega48, ATmega88, A←↩Tmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561, ATmega324←↩P, ATmega164P, ATmega644P, ATmega644,ATmega16HVA, ATtiny2313, ATtiny48, A←↩Ttiny261, ATtiny461, ATtiny861, AT90US←↩B162, AT90USB82, AT90USB1287, AT90←↩USB1286, AT90USB647, AT90USB646

TIMER0_C←↩OMPB_vect

SIG_OUT←↩PUT_CO←↩MPARE0B,SIG_OUTP←↩UT_COMPA←↩RE0_B

Timer Counter 0Compare MatchB

AT90PWM3, AT90PWM2, AT90PWM1, A←↩Tmega1284P, ATmega168P, ATmega328P,ATmega32HVB, ATmega48P, ATmega88←↩P, ATmega168, ATmega48, ATmega88,ATmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561, ATmega324←↩P, ATmega164P, ATmega644P, ATmega644,ATmega16HVA, ATtiny2313, ATtiny48, A←↩Ttiny261, ATtiny461, ATtiny861, AT90US←↩B162, AT90USB82, AT90USB1287, AT90←↩USB1286, AT90USB647, AT90USB646

TIMER0_C←↩OMP_A_vect

SIG_OUT←↩PUT_CO←↩MPARE0A,SIG_OUTP←↩UT_COMPA←↩RE0_A



TIMER0_C←↩OMP_vect

SIG_OUTP←↩UT_COMPA←↩RE0

Timer/Counter0Compare Match

AT90CAN128, AT90CAN32, AT90CAN64,ATmega103, ATmega128, ATmega16, A←↩Tmega161, ATmega162, ATmega165, A←↩Tmega165P, ATmega169, ATmega169←↩P, ATmega32, ATmega323, ATmega325,ATmega3250, ATmega3250P, ATmega329,ATmega3290, ATmega3290P, ATmega64,ATmega645, ATmega6450, ATmega649,ATmega6490, ATmega8515, ATmega8535

TIMER0_O←↩VF0_vect

SIG_OVER←↩FLOW0


AT90S2313, AT90S2323, AT90S2343, A←↩Ttiny22, ATtiny26

TIMER0_O←↩VF_vect

SIG_OVER←↩FLOW0


AT90S1200, AT90S2333, AT90S4414, A←↩T90S4433, AT90S4434, AT90S8515, A←↩T90S8535, AT90PWM216, AT90PWM2←↩B, AT90PWM316, AT90PWM3B, AT90P←↩WM3, AT90PWM2, AT90PWM1, AT90←↩CAN128, AT90CAN32, AT90CAN64, A←↩Tmega103, ATmega128, ATmega1284←↩P, ATmega16, ATmega161, ATmega162,ATmega163, ATmega165, ATmega165P,ATmega168P, ATmega169, ATmega169P,ATmega32, ATmega323, ATmega325, A←↩Tmega3250, ATmega3250P, ATmega328P,ATmega329, ATmega3290, ATmega3290←↩P, ATmega32HVB, ATmega48P, ATmega64,ATmega645, ATmega6450, ATmega649,ATmega6490, ATmega8, ATmega8515, A←↩Tmega8535, ATmega88P, ATmega168, A←↩Tmega48, ATmega88, ATmega640, A←↩Tmega1280, ATmega1281, ATmega2560,ATmega2561, ATmega324P, ATmega164←↩P, ATmega644P, ATmega644, ATmega16←↩HVA, ATtiny11, ATtiny12, ATtiny15, A←↩Ttiny2313, ATtiny28, ATtiny48, ATtiny261,ATtiny461, ATtiny861, AT90USB162, A←↩T90USB82, AT90USB1287, AT90USB1286,AT90USB647, AT90USB646

TIMER1_CA←↩PT1_vect



AT90S2313


214 CONTENTS



Timer/CounterCapture Event

AT90S2333, AT90S4414, AT90S4433,AT90S4434, AT90S8515, AT90S8535, A←↩T90PWM216, AT90PWM2B, AT90PWM316,AT90PWM3B, AT90PWM3, AT90PWM2,AT90PWM1, AT90CAN128, AT90CAN32,AT90CAN64, ATmega103, ATmega128,ATmega1284P, ATmega16, ATmega161,ATmega162, ATmega163, ATmega165,ATmega165P, ATmega168P, ATmega169,ATmega169P, ATmega32, ATmega323,ATmega325, ATmega3250, ATmega3250P,ATmega328P, ATmega329, ATmega3290,ATmega3290P, ATmega48P, ATmega64,ATmega645, ATmega6450, ATmega649,ATmega6490, ATmega8, ATmega8515,ATmega8535, ATmega88P, ATmega168,ATmega48, ATmega88, ATmega640, A←↩Tmega1280, ATmega1281, ATmega2560,ATmega2561, ATmega324P, ATmega164P,ATmega644P, ATmega644, ATtiny2313,ATtiny48, AT90USB162, AT90USB82,AT90USB1287, AT90USB1286, AT90US←↩B647, AT90USB646

TIMER1_C←↩MPA_vect


Timer/Counter1Compare Match1A

ATtiny26

TIMER1_C←↩MPB_vect


Timer/Counter1Compare Match1B

ATtiny26

TIMER1_C←↩OMP1_vect



AT90S2313




AT90S4414, AT90S4434, AT90S8515, A←↩T90S8535, AT90PWM216, AT90PWM2←↩B, AT90PWM316, AT90PWM3B, AT90P←↩WM3, AT90PWM2, AT90PWM1, AT90←↩CAN128, AT90CAN32, AT90CAN64, A←↩Tmega103, ATmega128, ATmega1284←↩P, ATmega16, ATmega161, ATmega162,ATmega163, ATmega165, ATmega165P,ATmega168P, ATmega169, ATmega169P,ATmega32, ATmega323, ATmega325, A←↩Tmega3250, ATmega3250P, ATmega328P,ATmega329, ATmega3290, ATmega3290←↩P, ATmega32HVB, ATmega48P, ATmega64,ATmega645, ATmega6450, ATmega649,ATmega6490, ATmega8, ATmega8515, A←↩Tmega8535, ATmega88P, ATmega168, A←↩Tmega48, ATmega88, ATmega640, A←↩Tmega1280, ATmega1281, ATmega2560,ATmega2561, ATmega324P, ATmega164P,ATmega644P, ATmega644, ATmega16HVA,ATtiny2313, ATtiny48, ATtiny261, ATtiny461,ATtiny861, AT90USB162, AT90USB82, A←↩T90USB1287, AT90USB1286, AT90US←↩B647, AT90USB646





Timer/Counter1CompareMatchB

AT90S4414, AT90S4434, AT90S8515, A←↩T90S8535, AT90PWM216, AT90PWM2←↩B, AT90PWM316, AT90PWM3B, AT90P←↩WM3, AT90PWM2, AT90PWM1, AT90←↩CAN128, AT90CAN32, AT90CAN64, A←↩Tmega103, ATmega128, ATmega1284←↩P, ATmega16, ATmega161, ATmega162,ATmega163, ATmega165, ATmega165P,ATmega168P, ATmega169, ATmega169P,ATmega32, ATmega323, ATmega325, A←↩Tmega3250, ATmega3250P, ATmega328P,ATmega329, ATmega3290, ATmega3290←↩P, ATmega32HVB, ATmega48P, ATmega64,ATmega645, ATmega6450, ATmega649,ATmega6490, ATmega8, ATmega8515, A←↩Tmega8535, ATmega88P, ATmega168, A←↩Tmega48, ATmega88, ATmega640, A←↩Tmega1280, ATmega1281, ATmega2560,ATmega2561, ATmega324P, ATmega164P,ATmega644P, ATmega644, ATmega16HVA,ATtiny2313, ATtiny48, ATtiny261, ATtiny461,ATtiny861, AT90USB162, AT90USB82, A←↩T90USB1287, AT90USB1286, AT90US←↩B647, AT90USB646

TIMER1_C←↩OMPC_vect

SIG_OUTP←↩UT_COMPA←↩RE1C

Timer/Counter1Compare MatchC

AT90CAN128, AT90CAN32, AT90CAN64,ATmega128, ATmega64, ATmega640, A←↩Tmega1280, ATmega1281, ATmega2560,ATmega2561, AT90USB162, AT90USB82,AT90USB1287, AT90USB1286, AT90US←↩B647, AT90USB646

TIMER1_C←↩OMPD_vect

SIG_OUTP←↩UT_COMPA←↩RE0D

Timer/Counter1Compare MatchD





AT90S2333, AT90S4433, ATtiny15

TIMER1_O←↩VF1_vect

SIG_OVER←↩FLOW1


AT90S2313, ATtiny26


SIG_OVER←↩FLOW1


AT90S2333, AT90S4414, AT90S4433,AT90S4434, AT90S8515, AT90S8535,AT90PWM216, AT90PWM2B, AT90←↩PWM316, AT90PWM3B, AT90PWM3,AT90PWM2, AT90PWM1, AT90CAN128,AT90CAN32, AT90CAN64, ATmega103,ATmega128, ATmega1284P, ATmega16,ATmega161, ATmega162, ATmega163,ATmega165, ATmega165P, ATmega168P,ATmega169, ATmega169P, ATmega32,ATmega323, ATmega325, ATmega3250,ATmega3250P, ATmega328P, ATmega329,ATmega3290, ATmega3290P, ATmega32←↩HVB, ATmega48P, ATmega64, ATmega645,ATmega6450, ATmega649, ATmega6490,ATmega8, ATmega8515, ATmega8535,ATmega88P, ATmega168, ATmega48,ATmega88, ATmega640, ATmega1280,ATmega1281, ATmega2560, ATmega2561,ATmega324P, ATmega164P, ATmega644P,ATmega644, ATmega16HVA, ATtiny15, A←↩Ttiny2313, ATtiny48, ATtiny261, ATtiny461,ATtiny861, AT90USB162, AT90USB82,AT90USB1287, AT90USB1286, AT90US←↩B647, AT90USB646


216 CONTENTS




ATmega168, ATmega48, ATmega88, A←↩Tmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561, ATmega324←↩P, ATmega164P, ATmega644P, ATmega644,AT90USB1287, AT90USB1286, AT90US←↩B647, AT90USB646




ATmega168, ATmega48, ATmega88, A←↩Tmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561, ATmega324←↩P, ATmega164P, ATmega644P, ATmega644,AT90USB1287, AT90USB1286, AT90US←↩B647, AT90USB646


SIG_OUTP←↩UT_COMPA←↩RE2


AT90S4434, AT90S8535, AT90CAN128,AT90CAN32, AT90CAN64, ATmega103,ATmega128, ATmega16, ATmega161, A←↩Tmega162, ATmega163, ATmega165, A←↩Tmega165P, ATmega169, ATmega169←↩P, ATmega32, ATmega323, ATmega325,ATmega3250, ATmega3250P, ATmega329,ATmega3290, ATmega3290P, ATmega64,ATmega645, ATmega6450, ATmega649,ATmega6490, ATmega8, ATmega8535


SIG_OVER←↩FLOW2


AT90S4434, AT90S8535, AT90CAN128,AT90CAN32, AT90CAN64, ATmega103,ATmega128, ATmega1284P, ATmega16,ATmega161, ATmega162, ATmega163, A←↩Tmega165, ATmega165P, ATmega168←↩P, ATmega169, ATmega169P, ATmega32,ATmega323, ATmega325, ATmega3250,ATmega3250P, ATmega328P, ATmega329,ATmega3290, ATmega3290P, ATmega48←↩P, ATmega64, ATmega645, ATmega6450,ATmega649, ATmega6490, ATmega8, A←↩Tmega8535, ATmega88P, ATmega168, A←↩Tmega48, ATmega88, ATmega640, A←↩Tmega1280, ATmega1281, ATmega2560,ATmega2561, ATmega324P, ATmega164P,ATmega644P, ATmega644, AT90USB1287,AT90USB1286, AT90USB647, AT90US←↩B646




AT90CAN128, AT90CAN32, AT90CAN64,ATmega128, ATmega1284P, ATmega162,ATmega64, ATmega640, ATmega1280, A←↩Tmega1281, ATmega2560, ATmega2561,AT90USB1287, AT90USB1286, AT90US←↩B647, AT90USB646












AT90CAN128, AT90CAN32, AT90CAN64,ATmega128, ATmega64, ATmega640, A←↩Tmega1280, ATmega1281, ATmega2560,ATmega2561, AT90USB1287, AT90US←↩B1286, AT90USB647, AT90USB646




SIG_OVER←↩FLOW3






ATmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561














SIG_OVER←↩FLOW4




















SIG_OVER←↩FLOW5



TWI_vect SIG_2WIRE←↩_SERIAL

2-wire Serial In-terface

AT90CAN128, AT90CAN32, AT90CAN64,ATmega128, ATmega1284P, ATmega16,ATmega163, ATmega168P, ATmega32, A←↩Tmega323, ATmega328P, ATmega32HVB,ATmega406, ATmega48P, ATmega64, A←↩Tmega8, ATmega8535, ATmega88P, A←↩Tmega168, ATmega48, ATmega88, A←↩Tmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561, ATmega324←↩P, ATmega164P, ATmega644P, ATmega644,ATtiny48, AT90USB1287, AT90USB1286,AT90USB647, AT90USB646

TXDONE_vect SIG_TXDO←↩NE

TransmissionDone, Bit TimerFlag 2 Interrupt

AT86RF401

TXEMPTY_←↩vect

SIG_TXBE Transmit BufferEmpty, Bit ItmerFlag 0 Interrupt

AT86RF401

UART0_RX←↩_vect

SIG_UART0←↩_RECV

UART0, Rx Com-plete

ATmega161

UART0_TX←↩_vect

SIG_UART0←↩_TRANS

UART0, Tx Com-plete

ATmega161

UART0_UD←↩RE_vect

SIG_UART0←↩_DATA

UART0 DataRegister Empty

ATmega161

UART1_RX←↩_vect


UART1, Rx Com-plete

ATmega161

UART1_TX←↩_vect


UART1, Tx Com-plete

ATmega161

UART1_UD←↩RE_vect


UART1 DataRegister Empty

ATmega161

UART_RX_←↩vect

SIG_UART_←↩RECV

UART, Rx Com-plete

AT90S2313, AT90S2333, AT90S4414, A←↩T90S4433, AT90S4434, AT90S8515, A←↩T90S8535, ATmega103, ATmega163, A←↩Tmega8515


218 CONTENTS

UART_TX_←↩vect

SIG_UART_←↩TRANS

UART, Tx Com-plete


UART_UDR←↩E_vect

SIG_UART_←↩DATA

UART Data Reg-ister Empty


USART0_R←↩XC_vect

SIG_USAR←↩T0_RECV

USART0, RxComplete

ATmega162

USART0_R←↩X_vect


USART0, RxComplete

AT90CAN128, AT90CAN32, AT90CAN64,ATmega128, ATmega1284P, ATmega165,ATmega165P, ATmega169, ATmega169←↩P, ATmega325, ATmega329, ATmega64,ATmega645, ATmega649, ATmega640, A←↩Tmega1280, ATmega1281, ATmega2560,ATmega2561, ATmega324P, ATmega164←↩P, ATmega644P, ATmega644

USART0_T←↩XC_vect

SIG_USAR←↩T0_TRANS

USART0, TxComplete

ATmega162

USART0_T←↩X_vect


USART0, TxComplete

AT90CAN128, AT90CAN32, AT90CAN64,ATmega128, ATmega1284P, ATmega165,ATmega165P, ATmega169, ATmega169P,ATmega325, ATmega3250, ATmega3250P,ATmega329, ATmega3290, ATmega3290P,ATmega64, ATmega645, ATmega6450, A←↩Tmega649, ATmega6490, ATmega640, A←↩Tmega1280, ATmega1281, ATmega2560,ATmega2561, ATmega324P, ATmega164←↩P, ATmega644P, ATmega644

USART0_U←↩DRE_vect


USART0 DataRegister Empty

AT90CAN128, AT90CAN32, AT90CAN64,ATmega128, ATmega1284P, ATmega162,ATmega165, ATmega165P, ATmega169,ATmega169P, ATmega325, ATmega329,ATmega64, ATmega645, ATmega649, A←↩Tmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561, ATmega324←↩P, ATmega164P, ATmega644P, ATmega644

USART1_R←↩XC_vect


USART1, RxComplete

ATmega162



USART1, RxComplete

AT90CAN128, AT90CAN32, AT90CAN64,ATmega128, ATmega1284P, ATmega64,ATmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561, ATmega324←↩P, ATmega164P, ATmega644P, ATmega644,AT90USB162, AT90USB82, AT90USB1287,AT90USB1286, AT90USB647, AT90US←↩B646

USART1_T←↩XC_vect


USART1, TxComplete

ATmega162



USART1, TxComplete

AT90CAN128, AT90CAN32, AT90CAN64,ATmega128, ATmega1284P, ATmega64,ATmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561, ATmega324←↩P, ATmega164P, ATmega644P, ATmega644,AT90USB162, AT90USB82, AT90USB1287,AT90USB1286, AT90USB647, AT90US←↩B646



USART1, DataRegister Empty

AT90CAN128, AT90CAN32, AT90CAN64,ATmega128, ATmega1284P, ATmega162,ATmega64, ATmega640, ATmega1280, A←↩Tmega1281, ATmega2560, ATmega2561,ATmega324P, ATmega164P, ATmega644←↩P, ATmega644, AT90USB162, AT90USB82,AT90USB1287, AT90USB1286, AT90US←↩B647, AT90USB646



USART2, RxComplete






USART2, TxComplete



SIG_USAR←↩T2_DATA

USART2 Dataregister Empty




USART3, RxComplete




USART3, TxComplete



SIG_USAR←↩T3_DATA

USART3 Dataregister Empty


USART_RX←↩C_vect

SIG_USA←↩RT_RECV,SIG_UART_←↩RECV

USART, Rx Com-plete

ATmega16, ATmega32, ATmega323, A←↩Tmega8

USART_RX←↩_vect

SIG_USA←↩RT_RECV,SIG_UART_←↩RECV

USART, Rx Com-plete

AT90PWM3, AT90PWM2, AT90PW←↩M1, ATmega168P, ATmega3250, A←↩Tmega3250P, ATmega328P, ATmega3290,ATmega3290P, ATmega48P, ATmega6450,ATmega6490, ATmega8535, ATmega88←↩P, ATmega168, ATmega48, ATmega88,ATtiny2313

USART_TX←↩C_vect

SIG_USA←↩RT_TRANS,SIG_UART_←↩TRANS

USART, Tx Com-plete

ATmega16, ATmega32, ATmega323, A←↩Tmega8

USART_TX←↩_vect

SIG_USA←↩RT_TRANS,SIG_UART_←↩TRANS

USART, Tx Com-plete

AT90PWM3, AT90PWM2, AT90PWM1,ATmega168P, ATmega328P, ATmega48P,ATmega8535, ATmega88P, ATmega168,ATmega48, ATmega88, ATtiny2313

USART_UD←↩RE_vect

SIG_USA←↩RT_DATA,SIG_UART_←↩DATA

USART DataRegister Empty

AT90PWM3, AT90PWM2, AT90PW←↩M1, ATmega16, ATmega168P, A←↩Tmega32, ATmega323, ATmega3250,ATmega3250P, ATmega328P, ATmega3290,ATmega3290P, ATmega48P, ATmega6450,ATmega6490, ATmega8, ATmega8535,ATmega88P, ATmega168, ATmega48,ATmega88, ATtiny2313

USI_OVER←↩FLOW_vect

SIG_USI_O←↩VERFLOW

USI Overflow ATmega165, ATmega165P, ATmega169,ATmega169P, ATmega325, ATmega3250,ATmega3250P, ATmega329, ATmega3290,ATmega3290P, ATmega645, ATmega6450,ATmega649, ATmega6490, ATtiny2313

USI_OVF_vect SIG_USI_O←↩VERFLOW

USI Overflow ATtiny26, ATtiny43U, ATtiny24, ATtiny44,ATtiny84, ATtiny45, ATtiny25, ATtiny85, A←↩Ttiny261, ATtiny461, ATtiny861

USI_START←↩_vect

SIG_USI_S←↩TART

USI Start Condi-tion

ATmega165, ATmega165P, ATmega169,ATmega169P, ATmega325, ATmega3250,ATmega3250P, ATmega329, ATmega3290,ATmega3290P, ATmega645, ATmega6450,ATmega649, ATmega6490, ATtiny2313, A←↩Ttiny43U, ATtiny45, ATtiny25, ATtiny85, A←↩Ttiny261, ATtiny461, ATtiny861

USI_STRT_←↩vect

SIG_USI_S←↩TART

USI Start ATtiny26

USI_STR_vect SIG_USI_S←↩TART

USI START ATtiny24, ATtiny44, ATtiny84

WATCHDO←↩G_vect

SIG_WATC←↩HDOG_TIM←↩EOUT

Watchdog Time-out


WDT_OVE←↩RFLOW_vect

SIG_WA←↩TCHDOG←↩_TIMEOUT,SIG_WDT_←↩OVERFLOW

Watchdog TimerOverflow

ATtiny2313


220 CONTENTS

WDT_vect SIG_WDT,SIG_WATC←↩HDOG_TIM←↩EOUT

Watchdog Time-out Interrupt

AT90PWM3, AT90PWM2, AT90PWM1, A←↩Tmega1284P, ATmega168P, ATmega328P,ATmega32HVB, ATmega406, ATmega48P,ATmega88P, ATmega168, ATmega48, A←↩Tmega88, ATmega640, ATmega1280, A←↩Tmega1281, ATmega2560, ATmega2561,ATmega324P, ATmega164P, ATmega644P,ATmega644, ATmega16HVA, ATtiny13, A←↩Ttiny43U, ATtiny48, ATtiny45, ATtiny25, A←↩Ttiny85, ATtiny261, ATtiny461, ATtiny861,AT90USB162, AT90USB82, AT90USB1287,AT90USB1286, AT90USB647, AT90US←↩B646


23.17.2.1 #define BADISR_vect


This is a vector which is aliased to __vector_default, the vector executed when an ISR fires with no accompanying ISRhandler. This may be used along with the ISR() macro to create a catch-all for undefined but used ISRs for debuggingpurposes.

23.17.2.2 #define cli( )

Disables all interrupts by clearing the global interrupt mask. This function actually compiles into a single line of assembly,so there is no function call overhead. However, the macro also implies a memory barrier which can cause additionalloss of optimization.

In order to implement atomic access to multi-byte objects, consider using the macros from <util/atomic.h>, rather thanimplementing them manually with cli() and sei().

23.17.2.3 #define EMPTY_INTERRUPT( vector )

Defines an empty interrupt handler function. This will not generate any prolog or epilog code and will only return fromthe ISR. Do not define a function body as this will define it for you. Example:

EMPTY_INTERRUPT(ADC_vect);

23.17.2.4 #define ISR( vector, attributes )

Introduces an interrupt handler function (interrupt service routine) that runs with global interrupts initially disabled bydefault with no attributes specified.

The attributes are optional and alter the behaviour and resultant generated code of the interrupt routine. Multipleattributes may be used for a single function, with a space seperating each attribute.

Valid attributes are ISR_BLOCK, ISR_NOBLOCK, ISR_NAKED and ISR_ALIASOF(vect).

vector must be one of the interrupt vector names that are valid for the particular MCU type.

23.17.2.5 #define ISR_ALIAS( vector, target_vector )

Aliases a given vector to another one in the same manner as the ISR_ALIASOF attribute for the ISR() macro. Unlikethe ISR_ALIASOF attribute macro however, this is compatible for all versions of GCC rather than just GCC version 4.2onwards.



Note

This macro creates a trampoline function for the aliased macro. This will result in a two cycle penalty for the aliasedvector compared to the ISR the vector is aliased to, due to the JMP/RJMP opcode used.

Deprecated For new code, the use of ISR(..., ISR_ALIASOF(...)) is recommended.

Example:

ISR(INT0_vect){

PORTB = 42;}

ISR_ALIAS(INT1_vect, INT0_vect);

23.17.2.6 #define ISR_ALIASOF( target_vector )

The ISR is linked to another ISR, specified by the vect parameter. This is compatible with GCC 4.2 and greater only.

Use this attribute in the attributes parameter of the ISR macro.

23.17.2.7 #define ISR_BLOCK

Identical to an ISR with no attributes specified. Global interrupts are initially disabled by the AVR hardware whenentering the ISR, without the compiler modifying this state.


23.17.2.8 #define ISR_NAKED

ISR is created with no prologue or epilogue code. The user code is responsible for preservation of the machine stateincluding the SREG register, as well as placing a reti() at the end of the interrupt routine.


23.17.2.9 #define ISR_NOBLOCK

ISR runs with global interrupts initially enabled. The interrupt enable flag is activated by the compiler as early as possiblewithin the ISR to ensure minimal processing delay for nested interrupts.

This may be used to create nested ISRs, however care should be taken to avoid stack overflows, or to avoid infinitelyentering the ISR for those cases where the AVR hardware does not clear the respective interrupt flag before enteringthe ISR.


23.17.2.10 #define reti( )

Returns from an interrupt routine, enabling global interrupts. This should be the last command executed before leavingan ISR defined with the ISR_NAKED attribute.

This macro actually compiles into a single line of assembly, so there is no function call overhead.

23.17.2.11 #define sei( )

Enables interrupts by setting the global interrupt mask. This function actually compiles into a single line of assembly, sothere is no function call overhead. However, the macro also implies a memory barrier which can cause additional lossof optimization.

In order to implement atomic access to multi-byte objects, consider using the macros from <util/atomic.h>, rather thanimplementing them manually with cli() and sei().


222 CONTENTS

23.17.2.12 #define SIGNAL( vector )

Introduces an interrupt handler function that runs with global interrupts initially disabled.

This is the same as the ISR macro without optional attributes.

Deprecated Do not use SIGNAL() in new code. Use ISR() instead.


23.18 <avr/io.h>: AVR device-specific IO definitions 223

23.18 <avr/io.h>: AVR device-specific IO definitions

Macros

• #define _PROTECTED_WRITE(reg, value)


#include <avr/io.h>

This header file includes the apropriate IO definitions for the device that has been specified by the -mmcu= compilercommand-line switch. This is done by diverting to the appropriate file <avr/ioXXXX.h> which should never beincluded directly. Some register names common to all AVR devices are defined directly within <avr/common.h>,which is included in <avr/io.h>, but most of the details come from the respective include file.

Note that this file always includes the following files:

#include <avr/sfr_defs.h>#include <avr/portpins.h>#include <avr/common.h>#include <avr/version.h>

See <avr/sfr_defs.h>: Special function registers for more details about that header file.

Included are definitions of the IO register set and their respective bit values as specified in the Atmel documentation.Note that inconsistencies in naming conventions, so even identical functions sometimes get different names on differentdevices.

Also included are the specific names useable for interrupt function definitions as documented here.

Finally, the following macros are defined:

• RAMENDThe last on-chip RAM address.

• XRAMENDThe last possible RAM location that is addressable. This is equal to RAMEND for devices that do not allow forexternal RAM. For devices that allow external RAM, this will be larger than RAMEND.

• E2ENDThe last EEPROM address.

• FLASHENDThe last byte address in the Flash program space.

• SPM_PAGESIZEFor devices with bootloader support, the flash pagesize (in bytes) to be used for the SPM instruction.

• E2PAGESIZEThe size of the EEPROM page.


224 CONTENTS


23.18.2.1 #define _PROTECTED_WRITE( reg, value )

Write value value to IO register reg that is protected through the Xmega configuration change protection (CCP)mechanism. This implements the timed sequence that is required for CCP.

Example to modify the CPU clock:

#include <avr/io.h>

_PROTECTED_WRITE(CLK_PSCTRL, CLK_PSADIV0_bm);_PROTECTED_WRITE(CLK_CTRL, CLK_SCLKSEL0_bm);


23.19 <avr/lock.h>: Lockbit Support 225

23.19 <avr/lock.h>: Lockbit Support

Introduction

The Lockbit API allows a user to specify the lockbit settings for the specific AVR device they are compiling for. Theselockbit settings will be placed in a special section in the ELF output file, after linking.

Programming tools can take advantage of the lockbit information embedded in the ELF file, by extracting this informationand determining if the lockbits need to be programmed after programming the Flash and EEPROM memories. This alsoallows a single ELF file to contain all the information needed to program an AVR.

To use the Lockbit API, include the <avr/io.h> header file, which in turn automatically includes the individual I/O headerfile and the <avr/lock.h> file. These other two files provides everything necessary to set the AVR lockbits.

Lockbit API

Each I/O header file may define up to 3 macros that controls what kinds of lockbits are available to the user.

If __LOCK_BITS_EXIST is defined, then two lock bits are available to the user and 3 mode settings are defined for thesetwo bits.

If __BOOT_LOCK_BITS_0_EXIST is defined, then the two BLB0 lock bits are available to the user and 4 mode settingsare defined for these two bits.

If __BOOT_LOCK_BITS_1_EXIST is defined, then the two BLB1 lock bits are available to the user and 4 mode settingsare defined for these two bits.

If __BOOT_LOCK_APPLICATION_TABLE_BITS_EXIST is defined then two lock bits are available to set the lockingmode for the Application Table Section (which is used in the XMEGA family).

If __BOOT_LOCK_APPLICATION_BITS_EXIST is defined then two lock bits are available to set the locking mode forthe Application Section (which is used in the XMEGA family).

If __BOOT_LOCK_BOOT_BITS_EXIST is defined then two lock bits are available to set the locking mode for the BootLoader Section (which is used in the XMEGA family).

The AVR lockbit modes have inverted values, logical 1 for an unprogrammed (disabled) bit and logical 0 for a pro-grammed (enabled) bit. The defined macros for each individual lock bit represent this in their definition by a bit-wiseinversion of a mask. For example, the LB_MODE_3 macro is defined as:

#define LB_MODE_3 (0xFC)‘

To combine the lockbit mode macros together to represent a whole byte,use the bitwise AND operator, like so:

(LB_MODE_3 & BLB0_MODE_2)

<avr/lock.h> also defines a macro that provides a default lockbit value: LOCKBITS_DEFAULT which is defined to be0xFF.

See the AVR device specific datasheet for more details about these lock bits and the available mode settings.

A convenience macro, LOCKMEM, is defined as a GCC attribute for a custom-named section of ".lock".

A convenience macro, LOCKBITS, is defined that declares a variable, __lock, of type unsigned char with the attributedefined by LOCKMEM. This variable allows the end user to easily set the lockbit data.


226 CONTENTS

Note

If a device-specific I/O header file has previously defined LOCKMEM, then LOCKMEM is not redefined. If adevice-specific I/O header file has previously defined LOCKBITS, then LOCKBITS is not redefined. LOCKBITS iscurrently known to be defined in the I/O header files for the XMEGA devices.

API Usage Example

Putting all of this together is easy:

#include <avr/io.h>

LOCKBITS = (LB_MODE_1 & BLB0_MODE_3 & BLB1_MODE_4);

int main(void){

return 0;}

Or:

#include <avr/io.h>

unsigned char __lock __attribute__((section (".lock"))) =(LB_MODE_1 & BLB0_MODE_3 & BLB1_MODE_4);

int main(void){

return 0;}

However there are a number of caveats that you need to be aware of touse this API properly.

Be sure to include <avr/io.h> to get all of the definitions for the API.The LOCKBITS macro defines a global variable to store the lockbit data. Thisvariable is assigned to its own linker section. Assign the desired lockbitvalues immediately in the variable initialization.

The .lock section in the ELF file will get its values from the initialvariable assignment ONLY. This means that you can NOT assign values tothis variable in functions and the new values will not be put into theELF .lock section.

The global variable is declared in the LOCKBITS macro has two leadingunderscores, which means that it is reserved for the "implementation",meaning the library, so it will not conflict with a user-named variable.

You must initialize the lockbit variable to some meaningful value, evenif it is the default value. This is because the lockbits default to alogical 1, meaning unprogrammed. Normal uninitialized data defaults to alllocgial zeros. So it is vital that all lockbits are initialized, even withdefault data. If they are not, then the lockbits may not programmed to thedesired settings and can possibly put your device into an unrecoverablestate.

Be sure to have the -mmcu=<em>device</em> flag in your compile command line andyour linker command line to have the correct device selected and to havethe correct I/O header file included when you include <avr/io.h>.

You can print out the contents of the .lock section in the ELF file byusing this command line:

avr-objdump -s -j .lock <ELF file>


23.20 <avr/pgmspace.h>: Program Space Utilities 227

23.20 <avr/pgmspace.h>: Program Space Utilities

Macros

• #define PROGMEM __ATTR_PROGMEM__• #define PGM_P const char ∗• #define PGM_VOID_P const void ∗• #define PSTR(s) ((const PROGMEM char ∗)(s))• #define pgm_read_byte_near(address_short) __LPM((uint16_t)(address_short))• #define pgm_read_word_near(address_short) __LPM_word((uint16_t)(address_short))• #define pgm_read_dword_near(address_short) __LPM_dword((uint16_t)(address_short))• #define pgm_read_float_near(address_short) __LPM_float((uint16_t)(address_short))• #define pgm_read_ptr_near(address_short) (void∗)__LPM_word((uint16_t)(address_short))• #define pgm_read_byte_far(address_long) __ELPM((uint32_t)(address_long))• #define pgm_read_word_far(address_long) __ELPM_word((uint32_t)(address_long))• #define pgm_read_dword_far(address_long) __ELPM_dword((uint32_t)(address_long))• #define pgm_read_float_far(address_long) __ELPM_float((uint32_t)(address_long))• #define pgm_read_ptr_far(address_long) (void∗)__ELPM_word((uint32_t)(address_long))• #define pgm_read_byte(address_short) pgm_read_byte_near(address_short)• #define pgm_read_word(address_short) pgm_read_word_near(address_short)• #define pgm_read_dword(address_short) pgm_read_dword_near(address_short)• #define pgm_read_float(address_short) pgm_read_float_near(address_short)• #define pgm_read_ptr(address_short) pgm_read_ptr_near(address_short)

Typedefs

• typedef void PROGMEM prog_void• typedef char PROGMEM prog_char• typedef unsigned char PROGMEM prog_uchar• typedef int8_t PROGMEM prog_int8_t• typedef uint8_t PROGMEM prog_uint8_t• typedef int16_t PROGMEM prog_int16_t• typedef uint16_t PROGMEM prog_uint16_t• typedef int32_t PROGMEM prog_int32_t• typedef uint32_t PROGMEM prog_uint32_t• typedef int64_t PROGMEM prog_int64_t• typedef uint64_t PROGMEM prog_uint64_t

Functions

• char ∗ strtok_P (char ∗s, PGM_P delim)• int memcmp_PF (const void ∗, uint_farptr_t, size_t) __ATTR_PURE__• void ∗ memcpy_PF (void ∗dest, uint_farptr_t src, size_t len)• int strcasecmp_PF (const char ∗s1, uint_farptr_t s2) __ATTR_PURE__• char ∗ strcat_PF (char ∗dest, uint_farptr_t src)• int strcmp_PF (const char ∗s1, uint_farptr_t s2) __ATTR_PURE__• char ∗ strcpy_PF (char ∗dest, uint_farptr_t src)• size_t strlcat_PF (char ∗dst, uint_farptr_t src, size_t siz)• size_t strlcpy_PF (char ∗dst, uint_farptr_t src, size_t siz)• size_t strlen_PF (uint_farptr_t src)


228 CONTENTS

• int strncasecmp_PF (const char ∗s1, uint_farptr_t s2, size_t n) __ATTR_PURE__• char ∗ strncat_PF (char ∗dest, uint_farptr_t src, size_t len)• int strncmp_PF (const char ∗s1, uint_farptr_t s2, size_t n) __ATTR_PURE__• char ∗ strncpy_PF (char ∗dest, uint_farptr_t src, size_t len)• size_t strnlen_PF (uint_farptr_t src, size_t len)• char ∗ strstr_PF (const char ∗s1, uint_farptr_t s2)


#include <avr/io.h>#include <avr/pgmspace.h>

The functions in this module provide interfaces for a program to access data stored in program space (flash memory) ofthe device. In order to use these functions, the target device must support either the LPM or ELPM instructions.

Note

These functions are an attempt to provide some compatibility with header files that come with IAR C, to makeporting applications between different compilers easier. This is not 100% compatibility though (GCC does nothave full support for multiple address spaces yet).If you are working with strings which are completely based in ram, use the standard string functions described in<string.h>: Strings.If possible, put your constant tables in the lower 64 KB and use pgm_read_byte_near() or pgm_read_word_near()instead of pgm_read_byte_far() or pgm_read_word_far() since it is more efficient that way, and you can still usethe upper 64K for executable code. All functions that are suffixed with a _P require their arguments to be in thelower 64 KB of the flash ROM, as they do not use ELPM instructions. This is normally not a big concern as thelinker setup arranges any program space constants declared using the macros from this header file so they areplaced right after the interrupt vectors, and in front of any executable code. However, it can become a problemif there are too many of these constants, or for bootloaders on devices with more than 64 KB of ROM. All thesefunctions will not work in that situation.For Xmega devices, make sure the NVM controller command register (NVM.CMD or NVM_CMD) is set to 0x00(NOP) before using any of these functions.


23.20.2.1 #define PGM_P const char ∗

Used to declare a variable that is a pointer to a string in program space.

23.20.2.2 #define pgm_read_byte( address_short ) pgm_read_byte_near(address_short)

Read a byte from the program space with a 16-bit (near) address.

Note

The address is a byte address. The address is in the program space.

23.20.2.3 #define pgm_read_byte_far( address_long ) __ELPM((uint32_t)(address_long))

Read a byte from the program space with a 32-bit (far) address.

Note




23.20.2.4 #define pgm_read_byte_near( address_short ) __LPM((uint16_t)(address_short))

Read a byte from the program space with a 16-bit (near) address.

Note


23.20.2.5 #define pgm_read_dword( address_short ) pgm_read_dword_near(address_short)

Read a double word from the program space with a 16-bit (near) address.

Note


23.20.2.6 #define pgm_read_dword_far( address_long ) __ELPM_dword((uint32_t)(address_long))

Read a double word from the program space with a 32-bit (far) address.

Note


23.20.2.7 #define pgm_read_dword_near( address_short ) __LPM_dword((uint16_t)(address_short))

Read a double word from the program space with a 16-bit (near) address.

Note


23.20.2.8 #define pgm_read_float( address_short ) pgm_read_float_near(address_short)

Read a float from the program space with a 16-bit (near) address.

Note


23.20.2.9 #define pgm_read_float_far( address_long ) __ELPM_float((uint32_t)(address_long))

Read a float from the program space with a 32-bit (far) address.

Note


23.20.2.10 #define pgm_read_float_near( address_short ) __LPM_float((uint16_t)(address_short))

Read a float from the program space with a 16-bit (near) address.

Note



230 CONTENTS

23.20.2.11 #define pgm_read_ptr( address_short ) pgm_read_ptr_near(address_short)

Read a pointer from the program space with a 16-bit (near) address.

Note


23.20.2.12 #define pgm_read_ptr_far( address_long ) (void∗)__ELPM_word((uint32_t)(address_long))

Read a pointer from the program space with a 32-bit (far) address.

Note


23.20.2.13 #define pgm_read_ptr_near( address_short ) (void∗)__LPM_word((uint16_t)(address_short))

Read a pointer from the program space with a 16-bit (near) address.

Note


23.20.2.14 #define pgm_read_word( address_short ) pgm_read_word_near(address_short)

Read a word from the program space with a 16-bit (near) address.

Note


23.20.2.15 #define pgm_read_word_far( address_long ) __ELPM_word((uint32_t)(address_long))

Read a word from the program space with a 32-bit (far) address.

Note


23.20.2.16 #define pgm_read_word_near( address_short ) __LPM_word((uint16_t)(address_short))

Read a word from the program space with a 16-bit (near) address.

Note


23.20.2.17 #define PGM_VOID_P const void ∗

Used to declare a generic pointer to an object in program space.

23.20.2.18 #define PROGMEM __ATTR_PROGMEM__

Attribute to use in order to declare an object being located in flash ROM.



23.20.2.19 #define PSTR( s ) ((const PROGMEM char ∗)(s))

Used to declare a static pointer to a string in program space.


23.20.3.1 prog_char

Note

DEPRECATED

This typedef is now deprecated because the usage of the progmem attribute on a type is not supported in GCC.However, the use of the progmem attribute on a variable declaration is supported, and this is now the recommendedusage.

The typedef is only visible if the macro PROG_TYPES_COMPAT has been defined before including <avr/pgmspace.h>(either by a #define directive, or by a -D compiler option.)

Type of a "char" object located in flash ROM.

23.20.3.2 prog_int16_t

Note

DEPRECATED



Type of an "int16_t" object located in flash ROM.

23.20.3.3 prog_int32_t

Note

DEPRECATED




23.20.3.4 prog_int64_t

Note

DEPRECATED



232 CONTENTS



Note


23.20.3.5 prog_int8_t

Note

DEPRECATED




23.20.3.6 prog_uchar

Note

DEPRECATED



Type of an "unsigned char" object located in flash ROM.

23.20.3.7 prog_uint16_t

Note

DEPRECATED



Type of an "uint16_t" object located in flash ROM.

23.20.3.8 prog_uint32_t



Note

DEPRECATED




23.20.3.9 prog_uint64_t

Note

DEPRECATED




Note


23.20.3.10 prog_uint8_t

Note

DEPRECATED




23.20.3.11 prog_void

Note

DEPRECATED



Type of a "void" object located in flash ROM. Does not make much sense by itself, but can be used to declare a "void ∗"object in flash ROM.


234 CONTENTS


23.20.4.1 int memcmp_PF ( const void ∗ s1, uint_farptr_t s2, size_t len )

Compare memory areas.

The memcmp_PF() function compares the first len bytes of the memory areas s1 and flash s2. The comparision isperformed using unsigned char operations. It is an equivalent of memcmp_P() function, except that it is capable workingon all FLASH including the exteded area above 64kB.

Returns

The memcmp_PF() function returns an integer less than, equal to, or greater than zero if the first len bytes of s1is found, respectively, to be less than, to match, or be greater than the first len bytes of s2.

23.20.4.2 void ∗ memcpy_PF ( void ∗ dest, uint_farptr_t src, size_t n )

Copy a memory block from flash to SRAM.

The memcpy_PF() function is similar to memcpy(), except the data is copied from the program space and is addressedusing a far pointer

\param dst A pointer to the destination buffer\param src A far pointer to the origin of data in flash memory\param n The number of bytes to be copied

Returns

The memcpy_PF() function returns a pointer to dst. The contents of RAMPZ SFR are undefined when the functionreturns

23.20.4.3 int strcasecmp_PF ( const char ∗ s1, uint_farptr_t s2 )


The strcasecmp_PF() function compares the two strings s1 and s2, ignoring the case of the characters

Parameters

s1 A pointer to the first string in SRAMs2 A far pointer to the second string in Flash

Returns

The strcasecmp_PF() function returns an integer less than, equal to, or greater than zero if s1 is found, respectively,to be less than, to match, or be greater than s2. The contents of RAMPZ SFR are undefined when the functionreturns

23.20.4.4 char ∗ strcat_PF ( char ∗ dst, uint_farptr_t src )

Concatenates two strings.

The strcat_PF() function is similar to strcat() except that the src string must be located in program space (flash) and isaddressed using a far pointer



Parameters

dst A pointer to the destination string in SRAMsrc A far pointer to the string to be appended in Flash

Returns

The strcat_PF() function returns a pointer to the resulting string dst. The contents of RAMPZ SFR are undefinedwhen the function returns

23.20.4.5 int strcmp_PF ( const char ∗ s1, uint_farptr_t s2 )

Compares two strings.

The strcmp_PF() function is similar to strcmp() except that s2 is a far pointer to a string in program space

Parameters

s1 A pointer to the first string in SRAMs2 A far pointer to the second string in Flash

Returns

The strcmp_PF() function returns an integer less than, equal to, or greater than zero if s1 is found, respectively,to be less than, to match, or be greater than s2. The contents of RAMPZ SFR are undefined when the functionreturns

23.20.4.6 char ∗ strcpy_PF ( char ∗ dst, uint_farptr_t src )

Duplicate a string.

The strcpy_PF() function is similar to strcpy() except that src is a far pointer to a string in program space

Parameters

dst A pointer to the destination string in SRAMsrc A far pointer to the source string in Flash

Returns

The strcpy_PF() function returns a pointer to the destination string dst. The contents of RAMPZ SFR are undefinedwhen the funcion returns

23.20.4.7 size_t strlcat_PF ( char ∗ dst, uint_farptr_t src, size_t n )


The strlcat_PF() function is similar to strlcat(), except that the src string must be located in program space (flash) and isaddressed using a far pointer

Appends src to string dst of size n (unlike strncat(), n is the full size of dst, not space left). At most n-1 characters willbe copied. Always NULL terminates (unless n <= strlen(dst))


236 CONTENTS

Parameters


n The total number of bytes allocated to the destination string

Returns

The strlcat_PF() function returns strlen(src) + MIN(n, strlen(initial dst)). If retval >= n, truncation occurred. Thecontents of RAMPZ SFR are undefined when the funcion returns

23.20.4.8 size_t strlcpy_PF ( char ∗ dst, uint_farptr_t src, size_t siz )

Copy a string from progmem to RAM.

Copy src to string dst of size siz. At most siz-1 characters will be copied. Always NULL terminates (unless siz == 0).

Returns

The strlcpy_PF() function returns strlen(src). If retval >= siz, truncation occurred. The contents of RAMPZ SFRare undefined when the function returns

23.20.4.9 size_t strlen_PF ( uint_farptr_t s )

Obtain the length of a string.

The strlen_PF() function is similar to strlen(), except that s is a far pointer to a string in program space

Parameters

s A far pointer to the string in flash

Returns

The strlen_PF() function returns the number of characters in s. The contents of RAMPZ SFR are undefined whenthe function returns

23.20.4.10 int strncasecmp_PF ( const char ∗ s1, uint_farptr_t s2, size_t n )


The strncasecmp_PF() function is similar to strcasecmp_PF(), except it only compares the first n characters of s1 andthe string in flash is addressed using a far pointer

Parameters

s1 A pointer to a string in SRAMs2 A far pointer to a string in Flashn The maximum number of bytes to compare

Returns

The strncasecmp_PF() function returns an integer less than, equal to, or greater than zero if s1 (or the first n bytesthereof) is found, respectively, to be less than, to match, or be greater than s2. The contents of RAMPZ SFR areundefined when the function returns



23.20.4.11 char ∗ strncat_PF ( char ∗ dst, uint_farptr_t src, size_t n )


The strncat_PF() function is similar to strncat(), except that the src string must be located in program space (flash) andis addressed using a far pointer

Parameters


n The maximum number of bytes to append

Returns

The strncat_PF() function returns a pointer to the resulting string dst. The contents of RAMPZ SFR are undefinedwhen the function returns

23.20.4.12 int strncmp_PF ( const char ∗ s1, uint_farptr_t s2, size_t n )

Compare two strings with limited length.

The strncmp_PF() function is similar to strcmp_PF() except it only compares the first (at most) n characters of s1 and s2

Parameters

s1 A pointer to the first string in SRAMs2 A far pointer to the second string in Flashn The maximum number of bytes to compare

Returns

The strncmp_PF() function returns an integer less than, equal to, or greater than zero if s1 (or the first n bytesthereof) is found, respectively, to be less than, to match, or be greater than s2. The contents of RAMPZ SFR areundefined when the function returns

23.20.4.13 char ∗ strncpy_PF ( char ∗ dst, uint_farptr_t src, size_t n )

Duplicate a string until a limited length.

The strncpy_PF() function is similar to strcpy_PF() except that not more than n bytes of src are copied. Thus, if there isno null byte among the first n bytes of src, the result will not be null-terminated

In the case where the length of src is less than that of n, the remainder of dst will be padded with nulls

Parameters


n The maximum number of bytes to copy

Returns

The strncpy_PF() function returns a pointer to the destination string dst. The contents of RAMPZ SFR are unde-fined when the function returns


238 CONTENTS

23.20.4.14 size_t strnlen_PF ( uint_farptr_t s, size_t len )

Determine the length of a fixed-size string.

The strnlen_PF() function is similar to strnlen(), except that s is a far pointer to a string in program space



Parameters

s A far pointer to the string in Flashlen The maximum number of length to return

Returns

The strnlen_PF function returns strlen_P(s), if that is less than len, or len if there is no ’\0’ character among thefirst len characters pointed to by s. The contents of RAMPZ SFR are undefined when the function returns

23.20.4.15 char ∗ strstr_PF ( const char ∗ s1, uint_farptr_t s2 )

Locate a substring.

The strstr_PF() function finds the first occurrence of the substring s2 in the string s1. The terminating ’\0’ charactersare not compared. The strstr_PF() function is similar to strstr() except that s2 is a far pointer to a string in programspace.

Returns

The strstr_PF() function returns a pointer to the beginning of the substring, or NULL if the substring is not found.If s2 points to a string of zero length, the function returns s1. The contents of RAMPZ SFR are undefined whenthe function returns

23.20.4.16 char∗ strtok_P ( char ∗ s, PGM_P delim )

Parses the string into tokens.

strtok_P() parses the string s into tokens. The first call to strtok_P() should have s as its first argument. Subsequentcalls should have the first argument set to NULL. If a token ends with a delimiter, this delimiting character is overwrittenwith a ’\0’ and a pointer to the next character is saved for the next call to strtok_P(). The delimiter string delim may bedifferent for each call.

The strtok_P() function is similar to strtok() except that delim is pointer to a string in program space.

Returns

The strtok_P() function returns a pointer to the next token or NULL when no more tokens are found.

Note

strtok_P() is NOT reentrant. For a reentrant version of this function see strtok_rP().


240 CONTENTS

23.21 <avr/power.h>: Power Reduction Management

#include <avr/power.h>

Many AVRs contain a Power Reduction Register (PRR) or Registers (PRRx) that allow you to reduce power consumptionby disabling or enabling various on-board peripherals as needed. Some devices have the XTAL Divide Control Register(XDIV) which offer similar functionality as System Clock Prescale Register (CLKPR).

There are many macros in this header file that provide an easy interface to enable or disable on-board peripherals toreduce power. See the table below.

Note

Not all AVR devices have a Power Reduction Register (for example the ATmega8). On those devices without aPower Reduction Register, the power reduction macros are not available..Not all AVR devices contain the same peripherals (for example, the LCD interface), or they will be named differently(for example, USART and USART0). Please consult your device’s datasheet, or the header file, to find out whichmacros are applicable to your device.For device using the XTAL Divide Control Register (XDIV), when prescaler is used, Timer/Counter0 can only beused in asynchronous mode. Keep in mind that Timer/Counter0 source shall be less than ¼th of peripheral clock.Therefore, when using a typical 32.768 kHz crystal, one shall not scale the clock below 131.072 kHz.

Power Macro Description Applicable for device

power_aca_disable() Disable the Analog Comparator on PortA. ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_aca_enable() Enable the Analog Comparator on PortA. ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_adc_enable() Enable the Analog to Digital Convertermodule.

ATmega640, ATmega1280, ATmega1281,ATmega1284, ATmega128RFA1,ATmega2560, ATmega2561, AT90USB646,AT90USB647, AT90USB1286,AT90USB1287, AT90PWM1, AT90PWM2,AT90PWM2B, AT90PWM3, AT90PWM3B,AT90PWM216, AT90PWM316,AT90PWM81, ATmega165, ATmega165P,ATmega325, ATmega325A, ATmega325PA,ATmega3250, ATmega3250A,ATmega3250PA, ATmega645,ATmega6450, ATmega169, ATmega169P,ATmega329, ATmega329A, ATmega3290,ATmega3290A, ATmega3290PA,ATmega649, ATmega6490, ATmega164P,ATmega324P, ATmega644, ATmega48,ATmega88, ATmega168, ATtiny24, ATtiny44,ATtiny84, ATtiny84A, ATtiny25, ATtiny45,ATtiny85, ATtiny261, ATtiny461, ATtiny861,ATmega256RFR2, ATmega2564RFR2,ATmega128RFR2, ATmega1284RFR2,ATmega64RFR2, ATmega644RFR2,ATxmega16A4U, ATxmega32A4U


23.21 <avr/power.h>: Power Reduction Management 241

power_adc_disable() Disable the Analog to Digital Convertermodule.

ATmega640, ATmega1280, ATmega1281,ATmega1284, ATmega128RFA1,ATmega2560, ATmega2561, AT90USB646,AT90USB647, AT90USB1286,AT90USB1287, AT90PWM1, AT90PWM2,AT90PWM2B, AT90PWM3, AT90PWM3B,AT90PWM216, AT90PWM316,AT90PWM81, ATmega165, ATmega165P,ATmega325, ATmega325A, ATmega325PA,ATmega3250, ATmega3250A, ATmega645,ATmega6450, ATmega169, ATmega169P,ATmega329, ATmega329A, ATmega3290,ATmega3290A, ATmega3290PA,ATmega649, ATmega6490, ATmega164P,ATmega324P, ATmega644, ATmega48,ATmega88, ATmega168, ATtiny24, ATtiny44,ATtiny84, ATtiny84A, ATtiny25, ATtiny45,ATtiny85, ATtiny261, ATtiny461, ATtiny861,ATmega256RFR2, ATmega2564RFR2,ATmega128RFR2, ATmega1284RFR2,ATmega64RFR2, ATmega644RFR2,ATxmega16A4U, ATxmega32A4U

power_adca_disable() Disable the Analog to Digital Convertermodule on PortA

ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_adca_enable() Enable the Analog to Digital Convertermodule on PortA


power_evsys_disable() Disable the EVSYS module ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_evsys_enable() Enable the EVSYS module ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_hiresc_disable() Disable the HIRES module on PortC ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_hiresc_enable() Enable the HIRES module on PortC ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_lcd_enable() Enable the LCD module. ATmega169, ATmega169P, ATmega329,ATmega329A, ATmega3290,ATmega3290A, ATmega649, ATmega6490,ATxmega64B1, ATxmega64B3,ATxmega128B3

power_lcd_disable(). Disable the LCD module. ATmega169, ATmega169P, ATmega329,ATmega329A, ATmega3290,ATmega3290A, ATmega649, ATmega6490,ATxmega64B1, ATxmega128B1,ATxmega64B3, ATxmega128B3

power_pga_enable() Enable the Programmable Gain Amplifiermodule.

ATmega256RFR2, ATmega2564RFR2,ATmega128RFR2, ATmega1284RFR2,ATmega64RFR2, ATmega644RFR2

power_pga_disable() Disable the Programmable Gain Amplifiermodule.

ATmega256RFR2, ATmega2564RFR2,ATmega128RFR2, ATmega1284RFR2,ATmega64RFR2, ATmega644RFR2


242 CONTENTS

power_pscr_enable() Enable the Reduced Power Stage Controllermodule.

AT90PWM81

power_pscr_disable() Disable the Reduced Power Stage Controllermodule.

AT90PWM81

power_psc0_enable() Enable the Power Stage Controller 0 module. AT90PWM1, AT90PWM2, AT90PWM2B,AT90PWM3, AT90PWM3B

power_psc0_disable() Disable the Power Stage Controller 0 module. AT90PWM1, AT90PWM2, AT90PWM2B,AT90PWM3, AT90PWM3B

power_psc1_enable() Enable the Power Stage Controller 1 module. AT90PWM1, AT90PWM2, AT90PWM2B,AT90PWM3, AT90PWM3B

power_psc1_disable() Disable the Power Stage Controller 1 module. AT90PWM1, AT90PWM2, AT90PWM2B,AT90PWM3, AT90PWM3B

power_psc2_enable() Enable the Power Stage Controller 2 module. AT90PWM1, AT90PWM2, AT90PWM2B,AT90PWM3, AT90PWM3B, AT90PWM81

power_psc2_disable() Disable the Power Stage Controller 2 module. AT90PWM1, AT90PWM2, AT90PWM2B,AT90PWM3, AT90PWM3B, AT90PWM81

power_ram0_enable() Enable the SRAM block 0 . ATmega256RFR2, ATmega2564RFR2,ATmega128RFR2, ATmega1284RFR2,ATmega64RFR2, ATmega644RFR2

power_ram0_disable() Disable the SRAM block 0. ATmega256RFR2, ATmega2564RFR2,ATmega128RFR2, ATmega1284RFR2,ATmega64RFR2, ATmega644RFR2







power_rtc_disable() Disable the RTC module ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_rtc_enable() Enable the RTC module ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3



power_spi_enable() Enable the Serial Peripheral Interfacemodule.

ATmega640, ATmega1280, ATmega1281,ATmega1284, ATmega128RFA1,ATmega2560, ATmega2561, AT90USB646,AT90USB647, AT90USB1286,AT90USB1287, AT90PWM1, AT90PWM2,AT90PWM2B, AT90PWM3, AT90PWM3B,AT90PWM216, AT90PWM316,AT90PWM81, ATmega165, ATmega165P,ATmega325, ATmega325A, ATmega325PA,ATmega3250, ATmega3250A,ATmega3250PA, ATmega645,ATmega6450, ATmega169, ATmega169P,ATmega329, ATmega329A, ATmega3290,ATmega3290A, ATmega3290PA,ATmega649, ATmega6490, ATmega164P,ATmega324P, ATmega644, ATmega48,ATmega88, ATmega168, ATmega256RFR2,ATmega2564RFR2, ATmega128RFR2,ATmega1284RFR2, ATmega64RFR2,ATmega644RFR2, ATxmega16A4U,ATxmega32A4U

power_spi_disable() Disable the Serial Peripheral Interfacemodule.

ATmega640, ATmega1280, ATmega1281,ATmega1284, ATmega128RFA1,ATmega2560, ATmega2561, AT90USB646,AT90USB647, AT90USB1286,AT90USB1287, AT90PWM1, AT90PWM2,AT90PWM2B, AT90PWM3, AT90PWM3B,AT90PWM216, AT90PWM316,AT90PWM81, ATmega165, ATmega165P,ATmega325, ATmega325A, ATmega325PA,ATmega3250, ATmega3250A,ATmega3250PA, ATmega645,ATmega6450, ATmega169, ATmega169P,ATmega329, ATmega329A, ATmega3290,ATmega3290A, ATmega3290PA,ATmega649, ATmega6490, ATmega164P,ATmega324P, ATmega644, ATmega48,ATmega88, ATmega168, ATmega256RFR2,ATmega2564RFR2, ATmega128RFR2,ATmega1284RFR2, ATmega64RFR2,ATmega644RFR2, ATxmega16A4U,ATxmega32A4U


244 CONTENTS

power_spic_disable() Disable the SPI module on PortC ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_spic_enable() Enable the SPI module on PortC ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_spid_disable() Disable the SPI module on PortD ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_spid_enable() Enable the SPI module on PortD ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_tc0c_disable() Disable the TC0 module on PortC ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_tc0c_enable() Enable the TC0 module on PortC ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_tc0d_disable() Disable the TC0 module on PortD ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_tc0d_enable() Enable the TC0 module on PortD ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_tc0e_disable() Disable the TC0 module on PortE ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_tc0e_enable() Enable the TC0 module on PortE ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_tc0f_disable() Disable the TC0 module on PortF ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_tc0f_enable() Enable the TC0 module on PortF ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_tc1c_disable() Disable the TC1 module on PortC ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_tc1c_enable() Enable the TC1 module on PortC ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3

power_twic_disable() Disable the Two Wire Interface module onPortC


power_twic_enable() Enable the Two Wire Interface module onPortC


power_twie_disable() Disable the Two Wire Interface module onPortE


power_twie_enable() Enable the Two Wire Interface module onPortE


power_timer0_enable() Enable the Timer 0 module. ATmega640, ATmega1280, ATmega1281,ATmega1284, ATmega128RFA1,ATmega2560, ATmega2561, AT90USB646,AT90USB647, AT90USB1286,AT90USB1287, AT90PWM1, AT90PWM216,AT90PWM316, AT90PWM2, AT90PWM2B,AT90PWM3, AT90PWM3B, ATmega165,ATmega165P, ATmega325, ATmega325A,ATmega3250, ATmega3250A, ATmega645,ATmega6450, ATmega164P, ATmega324P,ATmega644, ATmega406, ATmega48,ATmega88, ATmega168, ATtiny24, ATtiny44,ATtiny84, ATtiny84A, ATtiny25, ATtiny45,ATtiny85, ATtiny261, ATtiny461, ATtiny861,ATmega256RFR2, ATmega2564RFR2,ATmega128RFR2, ATmega1284RFR2,ATmega64RFR2, ATmega644RFR2,ATxmega16A4U, ATxmega32A4UGenerated on Tue Aug 12 2014 21:20:45 for avr-libc by Doxygen


power_timer0_disable() Disable the Timer 0 module. ATmega640, ATmega1280, ATmega1281,ATmega1284, ATmega128RFA1,ATmega2560, ATmega2561, AT90USB646,AT90USB647, AT90USB1286,AT90USB1287, AT90PWM1, AT90PWM2,AT90PWM2B, AT90PWM3, AT90PWM3B,AT90PWM216, AT90PWM316, ATmega165,ATmega165P, ATmega325, ATmega325A,ATmega3250, ATmega3250A, ATmega645,ATmega6450, ATmega164P, ATmega324P,ATmega644, ATmega406, ATmega48,ATmega88, ATmega168, ATtiny24, ATtiny44,ATtiny84, ATtiny84A, ATtiny25, ATtiny45,ATtiny85, ATtiny261, ATtiny461, ATtiny861,ATmega256RFR2, ATmega2564RFR2,ATmega128RFR2, ATmega1284RFR2,ATmega64RFR2, ATmega644RFR2,ATxmega16A4U, ATxmega32A4U

power_timer1_enable() Enable the Timer 1 module. ATmega640, ATmega1280, ATmega1281,ATmega1284, ATmega128RFA1,ATmega2560, ATmega2561, AT90USB646,AT90USB647, AT90USB1286,AT90USB1287, AT90PWM1, AT90PWM2,AT90PWM2B, AT90PWM3, AT90PWM3B,AT90PWM216, AT90PWM316,AT90PWM81, ATmega165, ATmega165P,ATmega325, ATmega325A, ATmega325PA,ATmega3250, ATmega3250A,ATmega3250PA, ATmega645,ATmega6450, ATmega169, ATmega169P,ATmega329, ATmega329A, ATmega3290,ATmega3290A, ATmega3290PA,ATmega649, ATmega6490, ATmega164P,ATmega324P, ATmega644, ATmega406,ATmega48, ATmega88, ATmega168,ATtiny24, ATtiny44, ATtiny84, ATtiny84A,ATtiny25, ATtiny45, ATtiny85, ATtiny261,ATtiny461, ATtiny861, ATmega256RFR2,ATmega2564RFR2, ATmega128RFR2,ATmega1284RFR2, ATmega64RFR2,ATmega644RFR2, ATxmega16A4U,ATxmega32A4U


246 CONTENTS

power_timer1_disable() Disable the Timer 1 module. ATmega640, ATmega1280, ATmega1281,ATmega1284, ATmega128RFA1,ATmega2560, ATmega2561, AT90USB646,AT90USB647, AT90USB1286,AT90USB1287, AT90PWM1, AT90PWM2,AT90PWM2B, AT90PWM3, AT90PWM3B,AT90PWM216, AT90PWM316,AT90PWM81, ATmega165, ATmega165P,ATmega325, ATmega325A, ATmega325PA,ATmega3250, ATmega3250A,ATmega3250PA, ATmega645,ATmega6450, ATmega169, ATmega169P,ATmega329, ATmega329A, ATmega3290,ATmega3290A, ATmega3290PA,ATmega649, ATmega6490, ATmega164P,ATmega324P, ATmega644, ATmega406,ATmega48, ATmega88, ATmega168,ATtiny24, ATtiny44, ATtiny84, ATtiny84A,ATtiny25, ATtiny45, ATtiny85, ATtiny261,ATtiny461, ATtiny861, ATmega256RFR2,ATmega2564RFR2, ATmega128RFR2,ATmega1284RFR2, ATmega64RFR2,ATmega644RFR2, ATxmega16A4U,ATxmega32A4U

power_timer2_enable() Enable the Timer 2 module. ATmega640, ATmega1280, ATmega1281,ATmega1284, ATmega128RFA1,ATmega2560, ATmega2561, AT90USB646,AT90USB647, AT90USB1286,AT90USB1287, ATmega164P,ATmega324P, ATmega644, ATmega48,ATmega88, ATmega168, ATmega256RFR2,ATmega2564RFR2, ATmega128RFR2,ATmega1284RFR2, ATmega64RFR2,ATmega644RFR2

power_timer2_disable() Disable the Timer 2 module. ATmega640, ATmega1280, ATmega1281,ATmega1284, ATmega128RFA1,ATmega2560, ATmega2561, AT90USB646,AT90USB647, AT90USB1286,AT90USB1287, ATmega164P,ATmega324P, ATmega644, ATmega48,ATmega88, ATmega168, ATmega256RFR2,ATmega2564RFR2, ATmega128RFR2,ATmega1284RFR2, ATmega64RFR2,ATmega644RFR2

power_timer3_enable() Enable the Timer 3 module. ATmega640, ATmega1280, ATmega1281,ATmega1284, ATmega128RFA1,ATmega2560, ATmega2561, AT90USB646,AT90USB647, AT90USB1286,AT90USB1287, ATmega256RFR2,ATmega2564RFR2, ATmega128RFR2,ATmega1284RFR2, ATmega64RFR2,ATmega644RFR2



power_timer3_disable() Disable the Timer 3 module. ATmega640, ATmega1280, ATmega1281,ATmega1284, ATmega128RFA1,ATmega2560, ATmega2561, AT90USB646,AT90USB647, AT90USB1286,AT90USB1287, ATmega256RFR2,ATmega2564RFR2, ATmega128RFR2,ATmega1284RFR2, ATmega64RFR2,ATmega644RFR2

power_timer4_enable() Enable the Timer 4 module. ATmega640, ATmega1280, ATmega1281,ATmega128RFA1, ATmega2560,ATmega2561, ATmega256RFR2,ATmega2564RFR2, ATmega128RFR2,ATmega1284RFR2, ATmega64RFR2,ATmega644RFR2

power_timer4_disable() Disable the Timer 4 module. ATmega640, ATmega1280, ATmega1281,ATmega128RFA1, ATmega2560,ATmega2561, ATmega256RFR2,ATmega2564RFR2, ATmega128RFR2,ATmega1284RFR2, ATmega64RFR2,ATmega644RFR2

power_timer5_enable() Enable the Timer 5 module. ATmega640, ATmega1280, ATmega1281,ATmega128RFA1, ATmega2560,ATmega2561, ATmega256RFR2,ATmega2564RFR2, ATmega128RFR2,ATmega1284RFR2, ATmega64RFR2,ATmega644RFR2

power_timer5_disable() Disable the Timer 5 module. ATmega640, ATmega1280, ATmega1281,ATmega128RFA1, ATmega2560,ATmega2561, ATmega256RFR2,ATmega2564RFR2, ATmega128RFR2,ATmega1284RFR2, ATmega64RFR2,ATmega644RFR2

power_twi_enable() Enable the Two Wire Interface module. ATmega640, ATmega1280, ATmega1281,ATmega1284, ATmega128RFA1,ATmega2560, ATmega2561, AT90USB646,AT90USB647, AT90USB1286,AT90USB1287, ATmega164P,ATmega324P, ATmega644, ATmega406,ATmega48, ATmega88, ATmega168,ATmega256RFR2, ATmega2564RFR2,ATmega128RFR2, ATmega1284RFR2,ATmega64RFR2, ATmega644RFR2,ATxmega16A4U, ATxmega32A4U

power_twi_disable() Disable the Two Wire Interface module. ATmega640, ATmega1280, ATmega1281,ATmega1284, ATmega128RFA1,ATmega2560, ATmega2561, AT90USB646,AT90USB647, AT90USB1286,AT90USB1287, ATmega164P,ATmega324P, ATmega644, ATmega406,ATmega48, ATmega88, ATmega168,ATmega256RFR2, ATmega2564RFR2,ATmega128RFR2, ATmega1284RFR2,ATmega64RFR2, ATmega644RFR2,ATxmega16A4U, ATxmega32A4U


248 CONTENTS

power_usart_enable() Enable the USART module. AT90PWM2, AT90PWM2B, AT90PWM3,AT90PWM3B

power_usart_disable() Disable the USART module. AT90PWM2, AT90PWM2B, AT90PWM3,AT90PWM3B

power_usart0_enable() Enable the USART 0 module. ATmega640, ATmega1280, ATmega1281,ATmega1284, ATmega128RFA1,ATmega2560, ATmega2561, ATmega165,ATmega165P, ATmega325, ATmega325A,ATmega325PA, ATmega3250,ATmega3250A, ATmega3250PA,ATmega645, ATmega6450, ATmega169,ATmega169P, ATmega329, ATmega329A,ATmega3290, ATmega3290A,ATmega3290PA, ATmega649,ATmega6490, ATmega164P, ATmega324P,ATmega644, ATmega48, ATmega88,ATmega168, ATmega256RFR2,ATmega2564RFR2, ATmega128RFR2,ATmega1284RFR2, ATmega64RFR2,ATmega644RFR2, ATxmega16A4U,ATxmega32A4U

power_usart0_disable() Disable the USART 0 module. ATmega640, ATmega1280, ATmega1281,ATmega1284, ATmega128RFA1,ATmega2560, ATmega2561, ATmega165,ATmega165P, ATmega325, ATmega325A,ATmega325PA, ATmega3250,ATmega3250A, ATmega3250PA,ATmega645, ATmega6450, ATmega169,ATmega169P, ATmega329, ATmega329A,ATmega3290, ATmega3290A,ATmega3290PA, ATmega649,ATmega6490, ATmega164P, ATmega324P,ATmega644, ATmega48, ATmega88,ATmega168, ATmega256RFR2,ATmega2564RFR2, ATmega128RFR2,ATmega1284RFR2, ATmega64RFR2,ATmega644RFR2, ATxmega16A4U,ATxmega32A4U

power_usart1_enable() Enable the USART 1 module. ATmega640, ATmega1280, ATmega1281,ATmega128RFA1, ATmega2560,ATmega2561, AT90USB646, AT90USB647,AT90USB1286, AT90USB1287,ATmega164P, ATmega324P, ATmega644,ATmega256RFR2, ATmega2564RFR2,ATmega128RFR2, ATmega1284RFR2,ATmega64RFR2, ATmega644RFR2,ATxmega16A4U, ATxmega32A4U



power_usart1_disable() Disable the USART 1 module. ATmega640, ATmega1280, ATmega1281,ATmega128RFA1, ATmega2560,ATmega2561, AT90USB646, AT90USB647,AT90USB1286, AT90USB1287,ATmega164P, ATmega324P, ATmega644,ATmega256RFR2, ATmega2564RFR2,ATmega128RFR2, ATmega1284RFR2,ATmega64RFR2, ATmega644RFR2,ATxmega16A4U, ATxmega32A4U

power_usart2_enable() Enable the USART 2 module. ATmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561

power_usart2_disable() Disable the USART 2 module. ATmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561

power_usart3_enable() Enable the USART 3 module. ATmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561

power_usart3_disable() Disable the USART 3 module. ATmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561

power_usartc0_disable() Disable the USART0 module on PortC ATmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561

power_usartc0_enable() Enable the USART0 module on PortC ATmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561

power_usartd0_disable() Disable the USART0 module on PortD ATmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561

power_usartd0_enable() Enable the USART0 module on PortD ATmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561

power_usarte0_disable() Disable the USART0 module on PortE ATmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561

power_usarte0_enable() Enable the USART0 module on PortE ATmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561

power_usartf0_disable() Disable the USART0 module on PortF ATmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561

power_usartf0_enable() Enable the USART0 module on PortF ATmega640, ATmega1280, ATmega1281,ATmega2560, ATmega2561

power_usb_enable() Enable the USB module. AT90USB646, AT90USB647,AT90USB1286, AT90USB1287,ATxmega64B1, ATxmega128B1,ATxmega64B3, ATxmega128B3,ATxmega16A4U, ATxmega32A4U,ATxmega128c3, ATxmega256c3,ATxmega16c4, ATxmega32c4


250 CONTENTS

power_usb_disable() Disable the USB module. AT90USB646, AT90USB647,AT90USB1286, AT90USB1287,ATxmega64B1, ATxmega128B1,ATxmega64B3, ATxmega128B3,ATxmega16A4U,ATxmega32A4U,ATxmega128c3,ATxmega256c3, ATxmega16c4,ATxmega32c4

power_usi_enable() Enable the Universal Serial Interface module. ATtiny24, ATtiny44, ATtiny84, ATtiny84A,ATtiny25, ATtiny45, ATtiny85, ATtiny261,ATtiny461, ATtiny861

power_usi_disable() Disable the Universal Serial Interface module. ATtiny24, ATtiny44, ATtiny84, ATtiny84A,ATtiny25, ATtiny45, ATtiny85, ATtiny261,ATtiny461, ATtiny861

power_vadc_enable() Enable the Voltage ADC module. ATmega406

power_vadc_disable() Disable the Voltage ADC module. ATmega406

power_all_enable() Enable all modules. ATxmega6A4, ATxmega32A4,ATxmega64A1, ATxmega64A1U,ATxmega64A3, ATxmegaA1, ATxmegaA1U,ATxmega128A3, ATxmega192A3,ATxmega256A3, ATxmegaA3B,ATxmega16D4, ATxmega32D4,ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3,ATmega640, ATmega1280, ATmega1281,ATmega128RFA1, ATmega2560,ATmega2561, AT90USB646, AT90USB647,AT90USB1286, AT90USB1287, AT90PWM1,AT90PWM2, AT90PWM2B, AT90PWM3,AT90PWM3B, AT90PWM216,AT90PWM316, ATmega165, ATmega165P,ATmega325, ATmega325A, ATmega325PA,ATmega3250, ATmega3250A,ATmega3250PA, ATmega645,ATmega6450, ATmega169, ATmega169P,ATmega329, ATmega329A, ATmega3290,ATmega3290A, ATmega3290PA,ATmega649, ATmega6490, ATmega164P,ATmega324P, ATmega644, ATmega406,ATmega48, ATmega88, ATmega168,ATtiny24, ATtiny44, ATtiny84, ATtiny84A,ATtiny25, ATtiny45, ATtiny85, ATtiny261,ATtiny461, ATtiny861, ATmega256RFR2,ATmega2564RFR2, ATmega128RFR2,ATmega1284RFR2, ATmega64RFR2,ATmega644RFR2, ATxmega64B1,ATxmega128B1, ATxmega64B3,ATxmega128B3, ATxmega16A4U,ATxmega32A4U, ATxmega64A3U,ATxmega128A3U, ATxmega192A3U,ATxmega256A3U



power_all_disable() Disable all modules. ATxmega6A4, ATxmega32A4,ATxmega64A1, ATxmega64A1U,ATxmega64A3, ATxmegaA1, ATxmegaA1U,ATxmega128A3, ATxmega192A3,ATxmega256A3, ATxmegaA3B,ATxmega16D4, ATxmega32D4,ATxmega64D3, ATxmega128D3,ATxmega192D3, ATxmega256D3,ATmega640, ATmega1280, ATmega1281,ATmega128RFA1, ATmega2560,ATmega2561, AT90USB646, AT90USB647,AT90USB1286, AT90USB1287, AT90PWM1,AT90PWM2, AT90PWM2B, AT90PWM3,AT90PWM3B, AT90PWM216,AT90PWM316, ATmega165, ATmega165P,ATmega325, ATmega325A, ATmega325PA,ATmega3250, ATmega3250A,ATmega3250PA, ATmega645,ATmega6450, ATmega169, ATmega169P,ATmega329, ATmega329A, ATmega3290,ATmega3290A, ATmega3290PA,ATmega649, ATmega6490, ATmega164P,ATmega324P, ATmega644, ATmega406,ATmega48, ATmega88, ATmega168,ATtiny24, ATtiny44, ATtiny84, ATtiny84A,ATtiny25, ATtiny45, ATtiny85, ATtiny261,ATtiny461, ATtiny861, ATmega256RFR2,ATmega2564RFR2, ATmega128RFR2,ATmega1284RFR2, ATmega64RFR2,ATmega644RFR2, ATxmega64B1,ATxmega128B1, ATxmega64B3,ATxmega128B3, ATxmega16A4U,ATxmega32A4U, ATxmega64A3U,ATxmega128A3U, ATxmega192A3U,ATxmega256A3U

Some of the newer AVRs contain a System Clock Prescale Register (CLKPR) that allows you to decrease the systemclock frequency and the power consumption when the need for processing power is low. On some earlier AVRs (A←↩Tmega103, ATmega64, ATmega128), similar functionality can be achieved through the XTAL Divide Control Register.Below are two macros and an enumerated type that can be used to interface to the Clock Prescale Register or XTALDivide Control Register.

Note

Not all AVR devices have a clock prescaler. On those devices without a Clock Prescale Register or XTAL DivideControl Register, these macros are not available.

typedef enum{

clock_div_1 = 0,clock_div_2 = 1,clock_div_4 = 2,clock_div_8 = 3,clock_div_16 = 4,clock_div_32 = 5,clock_div_64 = 6,clock_div_128 = 7,clock_div_256 = 8,clock_div_1_rc = 15, // ATmega128RFA1 only

} clock_div_t;

Clock prescaler setting enumerations for device using System Clock Prescale Register.

typedef enum{

clock_div_1 = 1,clock_div_2 = 2,


252 CONTENTS

clock_div_4 = 4,clock_div_8 = 8,clock_div_16 = 16,clock_div_32 = 32,clock_div_64 = 64,clock_div_128 = 128

} clock_div_t;

Clock prescaler setting enumerations for device using XTAL Divide Control Register.

clock_prescale_set(x)

Set the clock prescaler register select bits, selecting a system clock division setting. This function is inlined, even ifcompiler optimizations are disabled.

The type of x is clock_div_t.

Note

For device with XTAL Divide Control Register (XDIV), x can actually range from 1 to 129. Thus, one does notneed to use clock_div_t type as argument.

clock_prescale_get()

Gets and returns the clock prescaler register setting. The return type is clock_div_t.

Note

For device with XTAL Divide Control Register (XDIV), return can actually range from 1 to 129. Care should betaken has the return value could differ from the typedef enum clock_div_t. This should only happen if clock_←↩prescale_set was previously called with a value other than those defined by clock_div_t.


23.22 Additional notes from <avr/sfr_defs.h> 253

23.22 Additional notes from <avr/sfr_defs.h>

The <avr/sfr_defs.h> file is included by all of the <avr/ioXXXX.h> files, which use macros defined here tomake the special function register definitions look like C variables or simple constants, depending on the _SFR_ASM←↩_COMPAT define. Some examples from <avr/iocanxx.h> to show how to define such macros:

#define PORTA _SFR_IO8(0x02)#define EEAR _SFR_IO16(0x21)#define UDR0 _SFR_MEM8(0xC6)#define TCNT3 _SFR_MEM16(0x94)#define CANIDT _SFR_MEM32(0xF0)

If _SFR_ASM_COMPAT is not defined, C programs can use names like PORTA directly in C expressions (also on theleft side of assignment operators) and GCC will do the right thing (use short I/O instructions if possible). The __SFR←↩_OFFSET definition is not used in any way in this case.

Define _SFR_ASM_COMPAT as 1 to make these names work as simple constants (addresses of the I/O registers). Thisis necessary when included in preprocessed assembler (∗.S) source files, so it is done automatically if ASSEMBLER isdefined. By default, all addresses are defined as if they were memory addresses (used in lds/sts instructions). Touse these addresses in in/out instructions, you must subtract 0x20 from them.

For more backwards compatibility, insert the following at the start of your old assembler source file:

#define __SFR_OFFSET 0

This automatically subtracts 0x20 from I/O space addresses, but it’s a hack, so it is recommended to change yoursource: wrap such addresses in macros defined here, as shown below. After this is done, the __SFR_OFFSETdefinition is no longer necessary and can be removed.

Real example - this code could be used in a boot loader that is portable between devices with SPMCR at differentaddresses.

<avr/iom163.h>: #define SPMCR _SFR_IO8(0x37)<avr/iom128.h>: #define SPMCR _SFR_MEM8(0x68)

#if _SFR_IO_REG_P(SPMCR)out _SFR_IO_ADDR(SPMCR), r24

#elsests _SFR_MEM_ADDR(SPMCR), r24

#endif

You can use the in/out/cbi/sbi/sbic/sbis instructions, without the _SFR_IO_REG_P test, if you know thatthe register is in the I/O space (as with SREG, for example). If it isn’t, the assembler will complain (I/O address out ofrange 0...0x3f), so this should be fairly safe.

If you do not define __SFR_OFFSET (so it will be 0x20 by default), all special register addresses are defined as memoryaddresses (so SREG is 0x5f), and (if code size and speed are not important, and you don’t like the ugly #if above) youcan always use lds/sts to access them. But, this will not work if __SFR_OFFSET != 0x20, so use a different macro(defined only if __SFR_OFFSET == 0x20) for safety:

sts _SFR_ADDR(SPMCR), r24

In C programs, all 3 combinations of _SFR_ASM_COMPAT and __SFR_OFFSET are supported - the _SFR_ADD←↩R(SPMCR) macro can be used to get the address of the SPMCR register (0x57 or 0x68 depending on device).


254 CONTENTS

23.23 <avr/sfr_defs.h>: Special function registers

Modules

• Additional notes from <avr/sfr_defs.h>

Bit manipulation

• #define _BV(bit) (1 << (bit))

IO register bit manipulation

• #define bit_is_set(sfr, bit) (_SFR_BYTE(sfr) & _BV(bit))• #define bit_is_clear(sfr, bit) (!(_SFR_BYTE(sfr) & _BV(bit)))• #define loop_until_bit_is_set(sfr, bit) do { } while (bit_is_clear(sfr, bit))• #define loop_until_bit_is_clear(sfr, bit) do { } while (bit_is_set(sfr, bit))


When working with microcontrollers, many tasks usually consist of controlling internal peripherals, or external peripheralsthat are connected to the device. The entire IO address space is made available as memory-mapped IO, i.e. it can beaccessed using all the MCU instructions that are applicable to normal data memory. For most AVR devices, the IOregister space is mapped into the data memory address space with an offset of 0x20 since the bottom of this space isreserved for direct access to the MCU registers. (Actual SRAM is available only behind the IO register area, starting atsome specific address depending on the device.)

For example the user can access memory-mapped IO registers as if they were globally defined variables like this:

PORTA = 0x33;unsigned char foo = PINA;

The compiler will choose the correct instruction sequence to generate based on the address of the register beingaccessed.

The advantage of using the memory-mapped registers in C programs is that it makes the programs more portable toother C compilers for the AVR platform.

Note that special care must be taken when accessing some of the 16-bit timer IO registers where access from boththe main program and within an interrupt context can happen. See Why do some 16-bit timer registers sometimes gettrashed?.

Porting programs that use the deprecated sbi/cbi macros

Access to the AVR single bit set and clear instructions are provided via the standard C bit manipulation commands. Thesbi and cbi macros are no longer directly supported. sbi (sfr,bit) can be replaced by sfr |= _BV(bit) .

i.e.: sbi(PORTB, PB1); is now PORTB |= _BV(PB1);

This actually is more flexible than having sbi directly, as the optimizer will use a hardware sbi if appropriate, or aread/or/write operation if not appropriate. You do not need to keep track of which registers sbi/cbi will operate on.

Likewise, cbi (sfr,bit) is now sfr &= ∼(_BV(bit));


23.23 <avr/sfr_defs.h>: Special function registers 255


23.23.2.1 #define _BV( bit ) (1 << (bit))

#include <avr/io.h>

Converts a bit number into a byte value.

Note

The bit shift is performed by the compiler which then inserts the result into the code. Thus, there is no run-timeoverhead when using _BV().

23.23.2.2 #define bit_is_clear( sfr, bit ) (!(_SFR_BYTE(sfr) & _BV(bit)))

#include <avr/io.h>

Test whether bit bit in IO register sfr is clear. This will return non-zero if the bit is clear, and a 0 if the bit is set.

23.23.2.3 #define bit_is_set( sfr, bit ) (_SFR_BYTE(sfr) & _BV(bit))

#include <avr/io.h>

Test whether bit bit in IO register sfr is set. This will return a 0 if the bit is clear, and non-zero if the bit is set.

23.23.2.4 #define loop_until_bit_is_clear( sfr, bit ) do { } while (bit_is_set(sfr, bit))

#include <avr/io.h>

Wait until bit bit in IO register sfr is clear.

23.23.2.5 #define loop_until_bit_is_set( sfr, bit ) do { } while (bit_is_clear(sfr, bit))

#include <avr/io.h>

Wait until bit bit in IO register sfr is set.


256 CONTENTS

23.24 <avr/signature.h>: Signature Support

Introduction

The <avr/signature.h> header file allows the user to automatically and easily include the device’s signature data in aspecial section of the final linked ELF file.

This value can then be used by programming software to compare the on-device signature with the signature recordedin the ELF file to look for a match before programming the device.

API Usage Example

Usage is very simple; just include the header file:

#include <avr/signature.h>

This will declare a constant unsigned char array and it is initialized with the three signature bytes, MSB first, that aredefined in the device I/O header file. This array is then placed in the .signature section in the resulting linked ELF file.

The three signature bytes that are used to initialize the array are these defined macros in the device I/O header file, fromMSB to LSB: SIGNATURE_2, SIGNATURE_1, SIGNATURE_0.

This header file should only be included once in an application.


23.25 <avr/sleep.h>: Power Management and Sleep Modes 257

23.25 <avr/sleep.h>: Power Management and Sleep Modes

Functions

• void sleep_enable (void)• void sleep_disable (void)• void sleep_cpu (void)


#include <avr/sleep.h>

Use of the SLEEP instruction can allow an application to reduce its power comsumption considerably. AVR devices canbe put into different sleep modes. Refer to the datasheet for the details relating to the device you are using.

There are several macros provided in this header file to actually put the device into sleep mode. The simplest way is tooptionally set the desired sleep mode using set_sleep_mode() (it usually defaults to idle mode where the CPU isput on sleep but all peripheral clocks are still running), and then call sleep_mode(). This macro automatically setsthe sleep enable bit, goes to sleep, and clears the sleep enable bit.

Example:

#include <avr/sleep.h>

...set_sleep_mode(<mode>);sleep_mode();

Note that unless your purpose is to completely lock the CPU (until a hardware reset), interrupts need to be enabledbefore going to sleep.

As the sleep_mode() macro might cause race conditions in some situations, the individual steps of manipulatingthe sleep enable (SE) bit, and actually issuing the SLEEP instruction, are provided in the macros sleep_enable(),sleep_disable(), and sleep_cpu(). This also allows for test-and-sleep scenarios that take care of not missingthe interrupt that will awake the device from sleep.

Example:

#include <avr/interrupt.h>#include <avr/sleep.h>

...set_sleep_mode(<mode>);cli();if (some_condition){sleep_enable();sei();sleep_cpu();sleep_disable();

}sei();

This sequence ensures an atomic test of some_condition with interrupts being disabled. If the condition is met,sleep mode will be prepared, and the SLEEP instruction will be scheduled immediately after an SEI instruction. Asthe intruction right after the SEI is guaranteed to be executed before an interrupt could trigger, it is sure the device willreally be put to sleep.

Some devices have the ability to disable the Brown Out Detector (BOD) before going to sleep. This will also reducepower while sleeping. If the specific AVR device has this ability then an additional macro is defined: sleep_bod←↩_disable(). This macro generates inlined assembly code that will correctly implement the timed sequence for


258 CONTENTS

disabling the BOD before sleeping. However, there is a limited number of cycles after the BOD has been disabled thatthe device can be put into sleep mode, otherwise the BOD will not truly be disabled. Recommended practice is to disablethe BOD (sleep_bod_disable()), set the interrupts (sei()), and then put the device to sleep (sleep_cpu()),like so:

#include <avr/interrupt.h>#include <avr/sleep.h>

...set_sleep_mode(<mode>);cli();if (some_condition){sleep_enable();sleep_bod_disable();sei();sleep_cpu();sleep_disable();

}sei();


23.25.2.1 void sleep_cpu ( void )

Put the device into sleep mode. The SE bit must be set beforehand, and it is recommended to clear it afterwards.

23.25.2.2 void sleep_disable ( void )

Clear the SE (sleep enable) bit.

23.25.2.3 void sleep_enable ( void )

Put the device in sleep mode. How the device is brought out of sleep mode depends on the specific mode selected withthe set_sleep_mode() function. See the data sheet for your device for more details.

Set the SE (sleep enable) bit.


23.26 <avr/version.h>: avr-libc version macros 259

23.26 <avr/version.h>: avr-libc version macros

Macros

• #define __AVR_LIBC_VERSION_STRING__ "1.8.1"• #define __AVR_LIBC_VERSION__ 10801UL• #define __AVR_LIBC_DATE_STRING__ "20140811"• #define __AVR_LIBC_DATE_ 20140811UL• #define __AVR_LIBC_MAJOR__ 1• #define __AVR_LIBC_MINOR__ 8• #define __AVR_LIBC_REVISION__ 1


#include <avr/version.h>

This header file defines macros that contain version numbers and strings describing the current version of avr-libc.

The version number itself basically consists of three pieces that are separated by a dot: the major number, the minornumber, and the revision number. For development versions (which use an odd minor number), the string representationadditionally gets the date code (YYYYMMDD) appended.

This file will also be included by <avr/io.h>. That way, portable tests can be implemented using <avr/io.h>that can be used in code that wants to remain backwards-compatible to library versions prior to the date when the libraryversion API had been added, as referenced but undefined C preprocessor macros automatically evaluate to 0.


23.26.2.1 #define __AVR_LIBC_DATE_ 20140811UL

Numerical representation of the release date.

23.26.2.2 #define __AVR_LIBC_DATE_STRING__ "20140811"

String literal representation of the release date.

23.26.2.3 #define __AVR_LIBC_MAJOR__ 1

Library major version number.

23.26.2.4 #define __AVR_LIBC_MINOR__ 8

Library minor version number.

23.26.2.5 #define __AVR_LIBC_REVISION__ 1

Library revision number.

23.26.2.6 #define __AVR_LIBC_VERSION__ 10801UL

Numerical representation of the current library version.

In the numerical representation, the major number is multiplied by 10000, the minor number by 100, and all three partsare then added. It is intented to provide a monotonically increasing numerical value that can easily be used in numericalchecks.


260 CONTENTS

23.26.2.7 #define __AVR_LIBC_VERSION_STRING__ "1.8.1"

String literal representation of the current library version.


23.27 <avr/wdt.h>: Watchdog timer handling 261

23.27 <avr/wdt.h>: Watchdog timer handling

Macros

• #define wdt_reset() __asm__ __volatile__ ("wdr")

• #define wdt_enable(value)

• #define wdt_disable()

• #define WDTO_15MS 0






• #define WDTO_1S 6






This header file declares the interface to some inline macros handling the watchdog timer present in many AVR devices.In order to prevent the watchdog timer configuration from being accidentally altered by a crashing application, a specialtimed sequence is required in order to change it. The macros within this header file handle the required sequenceautomatically before changing any value. Interrupts will be disabled during the manipulation.

Note

Depending on the fuse configuration of the particular device, further restrictions might apply, in particular it mightbe disallowed to turn off the watchdog timer.

Note that for newer devices (ATmega88 and newer, effectively any AVR that has the option to also generate interrupts),the watchdog timer remains active even after a system reset (except a power-on condition), using the fastest prescalervalue (approximately 15 ms). It is therefore required to turn off the watchdog early during program startup, the datasheetrecommends a sequence like the following:

#include <stdint.h>#include <avr/wdt.h>

uint8_t mcusr_mirror __attribute__ ((section (".noinit")));

void get_mcusr(void) \__attribute__((naked)) \__attribute__((section(".init3")));

void get_mcusr(void){

mcusr_mirror = MCUSR;MCUSR = 0;wdt_disable();

}

Saving the value of MCUSR in mcusr_mirror is only needed if the application later wants to examine the resetsource, but in particular, clearing the watchdog reset flag before disabling the watchdog is required, according to thedatasheet.


262 CONTENTS


23.27.2.1 #define wdt_disable( )

Value:

__asm__ __volatile__ ( \"in __tmp_reg__, __SREG__" "\n\t" \"cli" "\n\t" \

"out %0, %1" "\n\t" \"out %0, __zero_reg__" "\n\t" \"out __SREG__,__tmp_reg__" "\n\t" \: /* no outputs */ \: "I" (_SFR_IO_ADDR(_WD_CONTROL_REG)), \"r" ((uint8_t)(_BV(_WD_CHANGE_BIT) | _BV(WDE))) \: "r0" \

)

Disable the watchdog timer, if possible. This attempts to turn off the Enable bit in the watchdog control register. See thedatasheet for details.

23.27.2.2 #define wdt_enable( value )

Value:

__asm__ __volatile__ ( \"in __tmp_reg__,__SREG__" "\n\t" \"cli" "\n\t" \"wdr" "\n\t" \"out %0,%1" "\n\t" \"out __SREG__,__tmp_reg__" "\n\t" \"out %0,%2" \: /* no outputs */ \: "I" (_SFR_IO_ADDR(_WD_CONTROL_REG)), \"r" ((uint8_t)(_BV(_WD_CHANGE_BIT) | _BV(WDE))), \"r" ((uint8_t) ((value & 0x08 ? _WD_PS3_MASK : 0x00) | \

_BV(WDE) | (value & 0x07)) ) \: "r0" \

)

Enable the watchdog timer, configuring it for expiry after timeout (which is a combination of the WDP0 through WDP2bits to write into the WDTCR register; For those devices that have a WDTCSR register, it uses the combination of theWDP0 through WDP3 bits).

See also the symbolic constants WDTO_15MS et al.

23.27.2.3 #define wdt_reset( ) __asm__ __volatile__ ("wdr")

Reset the watchdog timer. When the watchdog timer is enabled, a call to this instruction is required before the timerexpires, otherwise a watchdog-initiated device reset will occur.

23.27.2.4 #define WDTO_120MS 3

See WDT0_15MS


Symbolic constants for the watchdog timeout. Since the watchdog timer is based on a free-running RC oscillator, thetimes are approximate only and apply to a supply voltage of 5 V. At lower supply voltages, the times will increase. Forolder devices, the times will be as large as three times when operating at Vcc = 3 V, while the newer devices (e. g.ATmega128, ATmega8) only experience a negligible change.

Possible timeout values are: 15 ms, 30 ms, 60 ms, 120 ms, 250 ms, 500 ms, 1 s, 2 s. (Some devices also allow for 4 sand 8 s.) Symbolic constants are formed by the prefix WDTO_, followed by the time.


23.27 <avr/wdt.h>: Watchdog timer handling 263

Example that would select a watchdog timer expiry of approximately 500 ms:

wdt_enable(WDTO_500MS);

23.27.2.6 #define WDTO_1S 6

See WDT0_15MS


See WDT0_15MS

23.27.2.8 #define WDTO_2S 7

See WDT0_15MS


See WDT0_15MS

23.27.2.10 #define WDTO_4S 8

See WDT0_15MS Note: This is only available on the ATtiny2313, ATtiny24, ATtiny44, ATtiny84, ATtiny84A, A←↩Ttiny25, ATtiny45, ATtiny85, ATtiny261, ATtiny461, ATtiny861, ATmega48, ATmega88, ATmega168, ATmega48P,ATmega88P, ATmega168P, ATmega328P, ATmega164P, ATmega324P, ATmega644P, ATmega644, ATmega640,ATmega1280, ATmega1281, ATmega2560, ATmega2561, ATmega8HVA, ATmega16HVA, ATmega32HVB, A←↩Tmega406, ATmega1284P, AT90PWM1, AT90PWM2, AT90PWM2B, AT90PWM3, AT90PWM3B, AT90PWM216,AT90PWM316, AT90PWM81, AT90PWM161, AT90USB82, AT90USB162, AT90USB646, AT90USB647, AT90US←↩B1286, AT90USB1287, ATtiny48, ATtiny88.

23.27.2.11 #define WDTO_500MS 5

See WDT0_15MS


WDT0_15MS

23.27.2.13 #define WDTO_8S 9

See WDT0_15MS Note: This is only available on the ATtiny2313, ATtiny24, ATtiny44, ATtiny84, ATtiny84A, A←↩Ttiny25, ATtiny45, ATtiny85, ATtiny261, ATtiny461, ATtiny861, ATmega48, ATmega48A, ATmega48PA, ATmega88,ATmega168, ATmega48P, ATmega88P, ATmega168P, ATmega328P, ATmega164P, ATmega324P, ATmega644P, A←↩Tmega644, ATmega640, ATmega1280, ATmega1281, ATmega2560, ATmega2561, ATmega8HVA, ATmega16H←↩VA, ATmega32HVB, ATmega406, ATmega1284P, ATmega2564RFR2, ATmega256RFR2, ATmega1284RFR2, A←↩Tmega128RFR2, ATmega644RFR2, ATmega64RFR2 AT90PWM1, AT90PWM2, AT90PWM2B, AT90PWM3, AT90←↩PWM3B, AT90PWM216, AT90PWM316, AT90PWM81, AT90PWM161, AT90USB82, AT90USB162, AT90USB646,AT90USB647, AT90USB1286, AT90USB1287, ATtiny48, ATtiny88, ATxmega16a4u, ATxmega32a4u, ATxmega16c4,ATxmega32c4, ATxmega128c3, ATxmega192c3, ATxmega256c3.


264 CONTENTS

23.28 <util/atomic.h> Atomically and Non-Atomically Executed Code Blocks

Macros

• #define ATOMIC_BLOCK(type)• #define NONATOMIC_BLOCK(type)• #define ATOMIC_RESTORESTATE• #define ATOMIC_FORCEON• #define NONATOMIC_RESTORESTATE• #define NONATOMIC_FORCEOFF


#include <util/atomic.h>

Note

The macros in this header file require the ISO/IEC 9899:1999 ("ISO C99") feature of for loop variables that aredeclared inside the for loop itself. For that reason, this header file can only be used if the standard level of thecompiler (option –std=) is set to either c99 or gnu99.

The macros in this header file deal with code blocks that are guaranteed to be excuted Atomically or Non-Atmomically.The term "Atomic" in this context refers to the unability of the respective code to be interrupted.

These macros operate via automatic manipulation of the Global Interrupt Status (I) bit of the SREG register. Exit pathsfrom both block types are all managed automatically without the need for special considerations, i. e. the interrupt statuswill be restored to the same value it has been when entering the respective block.

A typical example that requires atomic access is a 16 (or more) bit variable that is shared between the main executionpath and an ISR. While declaring such a variable as volatile ensures that the compiler will not optimize accesses to itaway, it does not guarantee atomic access to it. Assuming the following example:

#include <inttypes.h>#include <avr/interrupt.h>#include <avr/io.h>

volatile uint16_t ctr;

ISR(TIMER1_OVF_vect){

ctr--;}

...intmain(void){

...ctr = 0x200;start_timer();while (ctr != 0)

// wait;

...}

There is a chance where the main context will exit its wait loop when the variable ctr just reached the value 0xFF. Thishappens because the compiler cannot natively access a 16-bit variable atomically in an 8-bit CPU. So the variable is forexample at 0x100, the compiler then tests the low byte for 0, which succeeds. It then proceeds to test the high byte, butthat moment the ISR triggers, and the main context is interrupted. The ISR will decrement the variable from 0x100 to0xFF, and the main context proceeds. It now tests the high byte of the variable which is (now) also 0, so it concludes thevariable has reached 0, and terminates the loop.


23.28 <util/atomic.h> Atomically and Non-Atomically Executed Code Blocks 265

Using the macros from this header file, the above code can be rewritten like:

#include <inttypes.h>#include <avr/interrupt.h>#include <avr/io.h>#include <util/atomic.h>

volatile uint16_t ctr;

ISR(TIMER1_OVF_vect){

ctr--;}

...intmain(void){

...ctr = 0x200;start_timer();sei();uint16_t ctr_copy;do{

ATOMIC_BLOCK(ATOMIC_FORCEON){ctr_copy = ctr;

}}while (ctr_copy != 0);...

}

This will install the appropriate interrupt protection before accessing variable ctr, so it is guaranteed to be consistentlytested. If the global interrupt state were uncertain before entering the ATOMIC_BLOCK, it should be executed with theparameter ATOMIC_RESTORESTATE rather than ATOMIC_FORCEON.

See Problems with reordering code for things to be taken into account with respect to compiler optimizations.


23.28.2.1 #define ATOMIC_BLOCK( type )

Creates a block of code that is guaranteed to be executed atomically. Upon entering the block the Global Interrupt Statusflag in SREG is disabled, and re-enabled upon exiting the block from any exit path.

Two possible macro parameters are permitted, ATOMIC_RESTORESTATE and ATOMIC_FORCEON.

23.28.2.2 #define ATOMIC_FORCEON

This is a possible parameter for ATOMIC_BLOCK. When used, it will cause the ATOMIC_BLOCK to force the state ofthe SREG register on exit, enabling the Global Interrupt Status flag bit. This saves on flash space as the previous valueof the SREG register does not need to be saved at the start of the block.

Care should be taken that ATOMIC_FORCEON is only used when it is known that interrupts are enabled before theblock’s execution or when the side effects of enabling global interrupts at the block’s completion are known and under-stood.

23.28.2.3 #define ATOMIC_RESTORESTATE

This is a possible parameter for ATOMIC_BLOCK. When used, it will cause the ATOMIC_BLOCK to restore the previousstate of the SREG register, saved before the Global Interrupt Status flag bit was disabled. The net effect of this is tomake the ATOMIC_BLOCK’s contents guaranteed atomic, without changing the state of the Global Interrupt Status flagwhen execution of the block completes.


266 CONTENTS

23.28.2.4 #define NONATOMIC_BLOCK( type )

Creates a block of code that is executed non-atomically. Upon entering the block the Global Interrupt Status flag inSREG is enabled, and disabled upon exiting the block from any exit path. This is useful when nested inside ATOMIC←↩_BLOCK sections, allowing for non-atomic execution of small blocks of code while maintaining the atomic access of theother sections of the parent ATOMIC_BLOCK.

Two possible macro parameters are permitted, NONATOMIC_RESTORESTATE and NONATOMIC_FORCEOFF.

23.28.2.5 #define NONATOMIC_FORCEOFF

This is a possible parameter for NONATOMIC_BLOCK. When used, it will cause the NONATOMIC_BLOCK to forcethe state of the SREG register on exit, disabling the Global Interrupt Status flag bit. This saves on flash space as theprevious value of the SREG register does not need to be saved at the start of the block.

Care should be taken that NONATOMIC_FORCEOFF is only used when it is known that interrupts are disabled beforethe block’s execution or when the side effects of disabling global interrupts at the block’s completion are known andunderstood.

23.28.2.6 #define NONATOMIC_RESTORESTATE

This is a possible parameter for NONATOMIC_BLOCK. When used, it will cause the NONATOMIC_BLOCK to restorethe previous state of the SREG register, saved before the Global Interrupt Status flag bit was enabled. The net effect ofthis is to make the NONATOMIC_BLOCK’s contents guaranteed non-atomic, without changing the state of the GlobalInterrupt Status flag when execution of the block completes.


23.29 <util/crc16.h>: CRC Computations 267

23.29 <util/crc16.h>: CRC Computations

Functions

• static __inline__ uint16_t _crc16_update (uint16_t __crc, uint8_t __data)• static __inline__ uint16_t _crc_xmodem_update (uint16_t __crc, uint8_t __data)• static __inline__ uint16_t _crc_ccitt_update (uint16_t __crc, uint8_t __data)• static __inline__ uint8_t _crc_ibutton_update (uint8_t __crc, uint8_t __data)• static __inline__ uint8_t _crc8_ccitt_update (uint8_t __crc, uint8_t __data)


#include <util/crc16.h>

This header file provides a optimized inline functions for calculating cyclic redundancy checks (CRC) using commonpolynomials.

References:

See the Dallas Semiconductor app note 27 for 8051 assembler example and general CRC optimization suggestions.The table on the last page of the app note is the key to understanding these implementations.

Jack Crenshaw’s "Implementing CRCs" article in the January 1992 isue of Embedded Systems Programming. This maybe difficult to find, but it explains CRC’s in very clear and concise terms. Well worth the effort to obtain a copy.

A typical application would look like:

// Dallas iButton test vector.uint8_t serno[] = { 0x02, 0x1c, 0xb8, 0x01, 0, 0, 0, 0xa2 };

intcheckcrc(void){

uint8_t crc = 0, i;

for (i = 0; i < sizeof serno / sizeof serno[0]; i++)crc = _crc_ibutton_update(crc, serno[i]);

return crc; // must be 0}


23.29.2.1 static __inline__ uint16_t _crc16_update ( uint16_t __crc, uint8_t __data ) [static]

Optimized CRC-16 calculation.

Polynomial: x∧16 + x∧15 + x∧2 + 1 (0xa001)Initial value: 0xffff

This CRC is normally used in disk-drive controllers.

The following is the equivalent functionality written in C.


268 CONTENTS

uint16_tcrc16_update(uint16_t crc, uint8_t a){

int i;

crc ^= a;for (i = 0; i < 8; ++i){

if (crc & 1)crc = (crc >> 1) ^ 0xA001;elsecrc = (crc >> 1);

}

return crc;}

23.29.2.2 static __inline__ uint8_t _crc8_ccitt_update ( uint8_t __crc, uint8_t __data ) [static]

Optimized CRC-8-CCITT calculation.

Polynomial: x∧8 + x∧2 + x + 1 (0xE0)

For use with simple CRC-8Initial value: 0x0

For use with CRC-8-ROHCInitial value: 0xffReference: http://tools.ietf.org/html/rfc3095#section-5.9.1

For use with CRC-8-ATM/ITUInitial value: 0xffFinal XOR value: 0x55Reference: http://www.itu.int/rec/T-REC-I.432.1-199902-I/en

The C equivalent has been originally written by Dave Hylands. Assembly code is based on _crc_ibutton_update opti-mization.


uint8_t_crc8_ccitt_update (uint8_t inCrc, uint8_t inData){

uint8_t i;uint8_t data;

data = inCrc ^ inData;

for ( i = 0; i < 8; i++ ){

if (( data & 0x80 ) != 0 ){

data <<= 1;data ^= 0x07;

}else{

data <<= 1;}

}return data;

}

23.29.2.3 static __inline__ uint16_t _crc_ccitt_update ( uint16_t __crc, uint8_t __data ) [static]

Optimized CRC-CCITT calculation.

Polynomial: x∧16 + x∧12 + x∧5 + 1 (0x8408)Initial value: 0xffff


http://tools.ietf.org/html/rfc3095#section-5.9.1

http://www.itu.int/rec/T-REC-I.432.1-199902-I/en

23.29 <util/crc16.h>: CRC Computations 269

This is the CRC used by PPP and IrDA.

See RFC1171 (PPP protocol) and IrDA IrLAP 1.1

Note

Although the CCITT polynomial is the same as that used by the Xmodem protocol, they are quite different. Thedifference is in how the bits are shifted through the alorgithm. Xmodem shifts the MSB of the CRC and the inputfirst, while CCITT shifts the LSB of the CRC and the input first.


uint16_tcrc_ccitt_update (uint16_t crc, uint8_t data){

data ^= lo8 (crc);data ^= data << 4;

return ((((uint16_t)data << 8) | hi8 (crc)) ^ (uint8_t)(data >> 4)^ ((uint16_t)data << 3));

}

23.29.2.4 static __inline__ uint8_t _crc_ibutton_update ( uint8_t __crc, uint8_t __data ) [static]

Optimized Dallas (now Maxim) iButton 8-bit CRC calculation.

Polynomial: x∧8 + x∧5 + x∧4 + 1 (0x8C)Initial value: 0x0

See http://www.maxim-ic.com/appnotes.cfm/appnote_number/27


uint8_t_crc_ibutton_update(uint8_t crc, uint8_t data){

uint8_t i;

crc = crc ^ data;for (i = 0; i < 8; i++){

if (crc & 0x01)crc = (crc >> 1) ^ 0x8C;

elsecrc >>= 1;

}

return crc;}

23.29.2.5 static __inline__ uint16_t _crc_xmodem_update ( uint16_t __crc, uint8_t __data ) [static]

Optimized CRC-XMODEM calculation.

Polynomial: x∧16 + x∧12 + x∧5 + 1 (0x1021)Initial value: 0x0

This is the CRC used by the Xmodem-CRC protocol.


uint16_tcrc_xmodem_update (uint16_t crc, uint8_t data){

int i;

crc = crc ^ ((uint16_t)data << 8);


http://www.maxim-ic.com/appnotes.cfm/appnote_number/27

270 CONTENTS

for (i=0; i<8; i++){

if (crc & 0x8000)crc = (crc << 1) ^ 0x1021;

elsecrc <<= 1;

}

return crc;}


23.30 <util/delay.h>: Convenience functions for busy-wait delay loops 271

23.30 <util/delay.h>: Convenience functions for busy-wait delay loops

Functions

• void _delay_ms (double __ms)• void _delay_us (double __us)


#define F_CPU 1000000UL // 1 MHz//#define F_CPU 14.7456E6#include <util/delay.h>

Note

As an alternative method, it is possible to pass the F_CPU macro down to the compiler from the Makefile. Obvi-ously, in that case, no #define statement should be used.

The functions in this header file are wrappers around the basic busy-wait functions from <util/delay_basic.h>. They aremeant as convenience functions where actual time values can be specified rather than a number of cycles to wait for.The idea behind is that compile-time constant expressions will be eliminated by compiler optimization so floating-pointexpressions can be used to calculate the number of delay cycles needed based on the CPU frequency passed by themacro F_CPU.

Note

In order for these functions to work as intended, compiler optimizations must be enabled, and the delay timemust be an expression that is a known constant at compile-time. If these requirements are not met, the resultingdelay will be much longer (and basically unpredictable), and applications that otherwise do not use floating-pointcalculations will experience severe code bloat by the floating-point library routines linked into the application.

The functions available allow the specification of microsecond, and millisecond delays directly, using the application-supplied macro F_CPU as the CPU clock frequency (in Hertz).


23.30.2.1 void _delay_ms ( double __ms )

Perform a delay of __ms milliseconds, using _delay_loop_2().

The macro F_CPU is supposed to be defined to a constant defining the CPU clock frequency (in Hertz).

The maximal possible delay is 262.14 ms / F_CPU in MHz.

When the user request delay which exceed the maximum possible one, _delay_ms() provides a decreased resolutionfunctionality. In this mode _delay_ms() will work with a resolution of 1/10 ms, providing delays up to 6.5535 seconds(independent from CPU frequency). The user will not be informed about decreased resolution.

If the avr-gcc toolchain has __builtin_avr_delay_cycles(unsigned long) support, maximal possible delay is 4294967.295ms/ F_CPU in MHz. For values greater than the maximal possible delay, overflows results in no delay i.e., 0ms.

Conversion of __us into clock cycles may not always result in integer. By default, the clock cycles rounded up to nextinteger. This ensures that the user gets atleast __us microseconds of delay.

Alternatively, user can define DELAY_ROUND_DOWN and DELAY_ROUND_CLOSEST to round down and round toclosest integer.


272 CONTENTS

Note: The new implementation of _delay_ms(double <strong>ms) with __builtin_avr_delay_cycles(unsigned long) sup-port is not backward compatible. User can define __DELAY_BACKWARD_COMPATIBLE to get a backward compatibledelay. Also, the backward compatible algorithm will be chosen if the code is compiled in a freestanding environment(GCC option -ffreestanding), as the math functions required for rounding are not available to the compiler then.

23.30.2.2 void _delay_us ( double __us )

Perform a delay of __us microseconds, using _delay_loop_1().

The macro F_CPU is supposed to be defined to a constant defining the CPU clock frequency (in Hertz).

The maximal possible delay is 768 us / F_CPU in MHz.

If the user requests a delay greater than the maximal possible one, _delay_us() will automatically call _delay_ms()instead. The user will not be informed about this case.

If the avr-gcc toolchain has __builtin_avr_delay_cycles(unsigned long) support, maximal possible delay is 4294967.295us/ F_CPU in MHz. For values greater than the maximal possible delay, overflow results in no delay i.e., 0us.

Conversion of __us into clock cycles may not always result in integer. By default, the clock cycles rounded up to nextinteger. This ensures that the user gets atleast __us microseconds of delay.

Alternatively, user can define DELAY_ROUND_DOWN and DELAY_ROUND_CLOSEST to round down and round toclosest integer.

Note: The new implementation of _delay_us(double <strong>us) with __builtin_avr_delay_cycles(unsigned long) sup-port is not backward compatible. User can define __DELAY_BACKWARD_COMPATIBLE to get a backward compatibledelay. Also, the backward compatible algorithm will be chosen if the code is compiled in a freestanding environment(GCC option -ffreestanding), as the math functions required for rounding are not available to the compiler then.


23.31 <util/delay_basic.h>: Basic busy-wait delay loops 273

23.31 <util/delay_basic.h>: Basic busy-wait delay loops

Functions

• void _delay_loop_1 (uint8_t __count)• void _delay_loop_2 (uint16_t __count)


#include <util/delay_basic.h>

The functions in this header file implement simple delay loops that perform a busy-waiting. They are typically used tofacilitate short delays in the program execution. They are implemented as count-down loops with a well-known CPUcycle count per loop iteration. As such, no other processing can occur simultaneously. It should be kept in mind that thefunctions described here do not disable interrupts.

In general, for long delays, the use of hardware timers is much preferrable, as they free the CPU, and allow for concurrentprocessing of other events while the timer is running. However, in particular for very short delays, the overhead of settingup a hardware timer is too much compared to the overall delay time.

Two inline functions are provided for the actual delay algorithms.


23.31.2.1 void _delay_loop_1 ( uint8_t __count )

Delay loop using an 8-bit counter __count, so up to 256 iterations are possible. (The value 256 would have to bepassed as 0.) The loop executes three CPU cycles per iteration, not including the overhead the compiler needs to setupthe counter register.

Thus, at a CPU speed of 1 MHz, delays of up to 768 microseconds can be achieved.

23.31.2.2 void _delay_loop_2 ( uint16_t __count )

Delay loop using a 16-bit counter __count, so up to 65536 iterations are possible. (The value 65536 would have tobe passed as 0.) The loop executes four CPU cycles per iteration, not including the overhead the compiler requires tosetup the counter register pair.

Thus, at a CPU speed of 1 MHz, delays of up to about 262.1 milliseconds can be achieved.


274 CONTENTS

23.32 <util/parity.h>: Parity bit generation

Macros

• #define parity_even_bit(val)


#include <util/parity.h>

This header file contains optimized assembler code to calculate the parity bit for a byte.


23.32.2.1 #define parity_even_bit( val )

Value:

(__extension__({ \unsigned char __t; \__asm__ ( \

"mov __tmp_reg__,%0" "\n\t" \"swap %0" "\n\t" \"eor %0,__tmp_reg__" "\n\t" \"mov __tmp_reg__,%0" "\n\t" \"lsr %0" "\n\t" \"lsr %0" "\n\t" \"eor %0,__tmp_reg__" \: "=r" (__t) \: "0" ((unsigned char)(val)) \: "r0" \

); \(((__t + 1) >> 1) & 1); \

}))

Returns

1 if val has an odd number of bits set.


23.33 <util/setbaud.h>: Helper macros for baud rate calculations 275

23.33 <util/setbaud.h>: Helper macros for baud rate calculations

Macros

• #define BAUD_TOL 2

• #define UBRR_VALUE

• #define UBRRL_VALUE

• #define UBRRH_VALUE

• #define USE_2X 0


#define F_CPU 11059200#define BAUD 38400#include <util/setbaud.h>

This header file requires that on entry values are already defined for F_CPU and BAUD. In addition, the macro BAUD←↩_TOL will define the baud rate tolerance (in percent) that is acceptable during the calculations. The value of BAUD_TOLwill default to 2 %.

This header file defines macros suitable to setup the UART baud rate prescaler registers of an AVR. All calculations aredone using the C preprocessor. Including this header file causes no other side effects so it is possible to include this filemore than once (supposedly, with different values for the BAUD parameter), possibly even within the same function.

Assuming that the requested BAUD is valid for the given F_CPU then the macro UBRR_VALUE is set to the requiredprescaler value. Two additional macros are provided for the low and high bytes of the prescaler, respectively: UBR←↩RL_VALUE is set to the lower byte of the UBRR_VALUE and UBRRH_VALUE is set to the upper byte. An additionalmacro USE_2X will be defined. Its value is set to 1 if the desired BAUD rate within the given tolerance could only beachieved by setting the U2X bit in the UART configuration. It will be defined to 0 if U2X is not needed.

Example usage:

#include <avr/io.h>

#define F_CPU 4000000

static voiduart_9600(void){#define BAUD 9600#include <util/setbaud.h>UBRRH = UBRRH_VALUE;UBRRL = UBRRL_VALUE;#if USE_2XUCSRA |= (1 << U2X);#elseUCSRA &= ~(1 << U2X);#endif}

static voiduart_38400(void){#undef BAUD // avoid compiler warning#define BAUD 38400#include <util/setbaud.h>UBRRH = UBRRH_VALUE;UBRRL = UBRRL_VALUE;#if USE_2XUCSRA |= (1 << U2X);#elseUCSRA &= ~(1 << U2X);#endif}


276 CONTENTS

In this example, two functions are defined to setup the UART to run at 9600 Bd, and 38400 Bd, respectively. Using aCPU clock of 4 MHz, 9600 Bd can be achieved with an acceptable tolerance without setting U2X (prescaler 25), while38400 Bd require U2X to be set (prescaler 12).


23.33.2.1 #define BAUD_TOL 2

Input and output macro for <util/setbaud.h>

Define the acceptable baud rate tolerance in percent. If not set on entry, it will be set to its default value of 2.

23.33.2.2 #define UBRR_VALUE

Output macro from <util/setbaud.h>

Contains the calculated baud rate prescaler value for the UBRR register.

23.33.2.3 #define UBRRH_VALUE


Contains the upper byte of the calculated prescaler value (UBRR_VALUE).

23.33.2.4 #define UBRRL_VALUE


Contains the lower byte of the calculated prescaler value (UBRR_VALUE).

23.33.2.5 #define USE_2X 0


Contains the value 1 if the desired baud rate tolerance could only be achieved by setting the U2X bit in the UARTconfiguration. Contains 0 otherwise.


23.34 <util/twi.h>: TWI bit mask definitions 277

23.34 <util/twi.h>: TWI bit mask definitions

TWSR values

Mnemonics:TW_MT_xxx - master transmitterTW_MR_xxx - master receiverTW_ST_xxx - slave transmitterTW_SR_xxx - slave receiver

• #define TW_START 0x08• #define TW_REP_START 0x10• #define TW_MT_SLA_ACK 0x18• #define TW_MT_SLA_NACK 0x20• #define TW_MT_DATA_ACK 0x28• #define TW_MT_DATA_NACK 0x30• #define TW_MT_ARB_LOST 0x38• #define TW_MR_ARB_LOST 0x38• #define TW_MR_SLA_ACK 0x40• #define TW_MR_SLA_NACK 0x48• #define TW_MR_DATA_ACK 0x50• #define TW_MR_DATA_NACK 0x58• #define TW_ST_SLA_ACK 0xA8• #define TW_ST_ARB_LOST_SLA_ACK 0xB0• #define TW_ST_DATA_ACK 0xB8• #define TW_ST_DATA_NACK 0xC0• #define TW_ST_LAST_DATA 0xC8• #define TW_SR_SLA_ACK 0x60• #define TW_SR_ARB_LOST_SLA_ACK 0x68• #define TW_SR_GCALL_ACK 0x70• #define TW_SR_ARB_LOST_GCALL_ACK 0x78• #define TW_SR_DATA_ACK 0x80• #define TW_SR_DATA_NACK 0x88• #define TW_SR_GCALL_DATA_ACK 0x90• #define TW_SR_GCALL_DATA_NACK 0x98• #define TW_SR_STOP 0xA0• #define TW_NO_INFO 0xF8• #define TW_BUS_ERROR 0x00• #define TW_STATUS_MASK• #define TW_STATUS (TWSR & TW_STATUS_MASK)

R/∼W bit in SLA+R/W address field.

• #define TW_READ 1• #define TW_WRITE 0


#include <util/twi.h>

This header file contains bit mask definitions for use with the AVR TWI interface.


278 CONTENTS


23.34.2.1 #define TW_BUS_ERROR 0x00

illegal start or stop condition

23.34.2.2 #define TW_MR_ARB_LOST 0x38

arbitration lost in SLA+R or NACK

23.34.2.3 #define TW_MR_DATA_ACK 0x50

data received, ACK returned

23.34.2.4 #define TW_MR_DATA_NACK 0x58

data received, NACK returned

23.34.2.5 #define TW_MR_SLA_ACK 0x40

SLA+R transmitted, ACK received

23.34.2.6 #define TW_MR_SLA_NACK 0x48

SLA+R transmitted, NACK received

23.34.2.7 #define TW_MT_ARB_LOST 0x38

arbitration lost in SLA+W or data

23.34.2.8 #define TW_MT_DATA_ACK 0x28

data transmitted, ACK received

23.34.2.9 #define TW_MT_DATA_NACK 0x30

data transmitted, NACK received

23.34.2.10 #define TW_MT_SLA_ACK 0x18

SLA+W transmitted, ACK received

23.34.2.11 #define TW_MT_SLA_NACK 0x20

SLA+W transmitted, NACK received

23.34.2.12 #define TW_NO_INFO 0xF8

no state information available

23.34.2.13 #define TW_READ 1

SLA+R address

23.34.2.14 #define TW_REP_START 0x10

repeated start condition transmitted


23.34 <util/twi.h>: TWI bit mask definitions 279

23.34.2.15 #define TW_SR_ARB_LOST_GCALL_ACK 0x78

arbitration lost in SLA+RW, general call received, ACK returned

23.34.2.16 #define TW_SR_ARB_LOST_SLA_ACK 0x68

arbitration lost in SLA+RW, SLA+W received, ACK returned

23.34.2.17 #define TW_SR_DATA_ACK 0x80

data received, ACK returned

23.34.2.18 #define TW_SR_DATA_NACK 0x88

data received, NACK returned

23.34.2.19 #define TW_SR_GCALL_ACK 0x70

general call received, ACK returned

23.34.2.20 #define TW_SR_GCALL_DATA_ACK 0x90

general call data received, ACK returned

23.34.2.21 #define TW_SR_GCALL_DATA_NACK 0x98

general call data received, NACK returned

23.34.2.22 #define TW_SR_SLA_ACK 0x60

SLA+W received, ACK returned

23.34.2.23 #define TW_SR_STOP 0xA0

stop or repeated start condition received while selected

23.34.2.24 #define TW_ST_ARB_LOST_SLA_ACK 0xB0

arbitration lost in SLA+RW, SLA+R received, ACK returned

23.34.2.25 #define TW_ST_DATA_ACK 0xB8

data transmitted, ACK received

23.34.2.26 #define TW_ST_DATA_NACK 0xC0

data transmitted, NACK received

23.34.2.27 #define TW_ST_LAST_DATA 0xC8

last data byte transmitted, ACK received

23.34.2.28 #define TW_ST_SLA_ACK 0xA8

SLA+R received, ACK returned


280 CONTENTS

23.34.2.29 #define TW_START 0x08

start condition transmitted

23.34.2.30 #define TW_STATUS (TWSR & TW_STATUS_MASK)

TWSR, masked by TW_STATUS_MASK

23.34.2.31 #define TW_STATUS_MASK

Value:

(_BV(TWS7)|_BV(TWS6)|_BV(TWS5)|_BV(TWS4)|\_BV(TWS3))

The lower 3 bits of TWSR are reserved on the ATmega163. The 2 LSB carry the prescaler bits on the newer ATmegas.

23.34.2.32 #define TW_WRITE 0

SLA+W address


23.35 <compat/deprecated.h>: Deprecated items 281

23.35 <compat/deprecated.h>: Deprecated items

Allowing specific system-wide interrupts

In addition to globally enabling interrupts, each device’s particular interrupt needs to be enabled separately if interruptsfor this device are desired. While some devices maintain their interrupt enable bit inside the device’s register set, externaland timer interrupts have system-wide configuration registers.

Example:

// Enable timer 1 overflow interrupts.timer_enable_int(_BV(TOIE1));

// Do some work...

// Disable all timer interrupts.timer_enable_int(0);

Note

Be careful when you use these functions. If you already have a different interrupt enabled, you could inadvertantlydisable it by enabling another intterupt.

• static __inline__ void timer_enable_int (unsigned char ints)• #define enable_external_int(mask) (__EICR = mask)• #define INTERRUPT(signame)• #define __INTR_ATTRS used

Obsolete IO macros

Back in a time when AVR-GCC and avr-libc could not handle IO port access in the direct assignment form as theyare handled now, all IO port access had to be done through specific macros that eventually resulted in inline assemblyinstructions performing the desired action.

These macros became obsolete, as reading and writing IO ports can be done by simply using the IO port name inan expression, and all bit manipulation (including those on IO ports) can be done using generic C bit manipulationoperators.

The macros in this group simulate the historical behaviour. While they are supposed to be applied to IO ports, theemulation actually uses standard C methods, so they could be applied to arbitrary memory locations as well.

• #define inp(port) (port)• #define outp(val, port) (port) = (val)• #define inb(port) (port)• #define outb(port, val) (port) = (val)• #define sbi(port, bit) (port) |= (1 << (bit))• #define cbi(port, bit) (port) &= ∼(1 << (bit))


This header file contains several items that used to be available in previous versions of this library, but have eventuallybeen deprecated over time.

#include <compat/deprecated.h>

These items are supplied within that header file for backward compatibility reasons only, so old source code that hasbeen written for previous library versions could easily be maintained until its end-of-life. Use of any of these items innew code is strongly discouraged.


282 CONTENTS


23.35.2.1 #define cbi( port, bit ) (port) &=∼(1 << (bit))

Deprecated

Clear bit in IO port port.

23.35.2.2 #define enable_external_int( mask ) (__EICR = mask)

Deprecated

This macro gives access to the GIMSK register (or EIMSK register if using an AVR Mega device or GICR register forothers). Although this macro is essentially the same as assigning to the register, it does adapt slightly to the type ofdevice being used. This macro is unavailable if none of the registers listed above are defined.

23.35.2.3 #define inb( port ) (port)

Deprecated

Read a value from an IO port port.

23.35.2.4 #define inp( port ) (port)

Deprecated

Read a value from an IO port port.

23.35.2.5 #define INTERRUPT( signame )

Value:

void signame (void) __attribute__ ((interrupt,__INTR_ATTRS)); \void signame (void)

Deprecated

Introduces an interrupt handler function that runs with global interrupts initially enabled. This allows interrupt handlersto be interrupted.

As this macro has been used by too many unsuspecting people in the past, it has been deprecated, and will be removedin a future version of the library. Users who want to legitimately re-enable interrupts in their interrupt handlers as quicklyas possible are encouraged to explicitly declare their handlers as described above.

23.35.2.6 #define outb( port, val ) (port) = (val)

Deprecated

Write val to IO port port.

23.35.2.7 #define outp( val, port ) (port) = (val)

Deprecated

Write val to IO port port.


23.35 <compat/deprecated.h>: Deprecated items 283

23.35.2.8 #define sbi( port, bit ) (port) |= (1 << (bit))

Deprecated

Set bit in IO port port.


23.35.3.1 static __inline__ void timer_enable_int ( unsigned char ints ) [static]

Deprecated

This function modifies the \c timsk register.The value you pass via \c ints is device specific.


284 CONTENTS

23.36 <compat/ina90.h>: Compatibility with IAR EWB 3.x

#include <compat/ina90.h>

This is an attempt to provide some compatibility with header files that come with IAR C, to make porting applicationsbetween different compilers easier. No 100% compatibility though.

Note

For actual documentation, please see the IAR manual.


23.37 Demo projects 285

23.37 Demo projects

Modules

• Combining C and assembly source files• A simple project• A more sophisticated project• Using the standard IO facilities• Example using the two-wire interface (TWI)


Various small demo projects are provided to illustrate several aspects of using the opensource utilities for the AV←↩R controller series. It should be kept in mind that these demos serve mainly educational purposes, and are normallynot directly suitable for use in any production environment. Usually, they have been kept as simple as sufficient todemonstrate one particular feature.

The simple project is somewhat like the "Hello world!" application for a microcontroller, about the most simple projectthat can be done. It is explained in good detail, to allow the reader to understand the basic concepts behind using thetools on an AVR microcontroller.

The more sophisticated demo project builds on top of that simple project, and adds some controls to it. It touches anumber of avr-libc’s basic concepts on its way.

A comprehensive example on using the standard IO facilities intends to explain that complex topic, using a practical mi-crocontroller peripheral setup with one RS-232 connection, and an HD44780-compatible industry-standard LCD display.

The Example using the two-wire interface (TWI) project explains the use of the two-wire hardware interface (also knownas "I2C") that is present on many AVR controllers.

Finally, the Combining C and assembly source files demo shows how C and assembly language source files can collab-orate within one project. While the overall project is managed by a C program part for easy maintenance, time-criticalparts are written directly in manually optimized assembly language for shortest execution times possible. Naturally,this kind of project is very closely tied to the hardware design, thus it is custom-tailored to a particular controller typeand peripheral setup. As an alternative to the assembly-language solution, this project also offers a C-only imple-mentation (deploying the exact same peripheral setup) based on a more sophisticated (and thus more expensive) butpin-compatible controller.

While the simple demo is meant to run on about any AVR setup possible where a LED could be connected to theOCR1[A] output, the large and stdio demos are mainly targeted to the Atmel STK500 starter kit, and the TWI examplerequires a controller where some 24Cxx two-wire EEPPROM can be connected to. For the STK500 demos, the defaultCPU (either an AT90S8515 or an ATmega8515) should be removed from its socket, and the ATmega16 that ships withthe kit should be inserted into socket SCKT3100A3. The ATmega16 offers an on-board ADC that is used in the largedemo, and all AVRs with an ADC feature a different pinout than the industry-standard compatible devices.

In order to fully utilize the large demo, a female 10-pin header with cable, connecting to a 10 kOhm potentiometer willbe useful.

For the stdio demo, an industry-standard HD44780-compatible LCD display of at least 16x1 characters will be needed.Among other things, the LCD4Linux project page describes many things around these displays, including commonpinouts.


http://ssl.bulix.org/projects/lcd4linux/

286 CONTENTS

23.38 Combining C and assembly source files

For time- or space-critical applications, it can often be desirable to combine C code (for easy maintenance) and assemblycode (for maximal speed or minimal code size) together. This demo provides an example of how to do that.

The objective of the demo is to decode radio-controlled model PWM signals, and control an output PWM based onthe current input signal’s value. The incoming PWM pulses follow a standard encoding scheme where a pulse width of920 microseconds denotes one end of the scale (represented as 0 % pulse width on output), and 2120 microsecondsmark the other end (100 % output PWM). Normally, multiple channels would be encoded that way in subsequent pulses,followed by a larger gap, so the entire frame will repeat each 14 through 20 ms, but this is ignored for the purpose of thedemo, so only a single input PWM channel is assumed.

The basic challenge is to use the cheapest controller available for the task, an ATtiny13 that has only a single timerchannel. As this timer channel is required to run the outgoing PWM signal generation, the incoming PWM decoding hadto be adjusted to the constraints set by the outgoing PWM.

As PWM generation toggles the counting direction of timer 0 between up and down after each 256 timer cycles, thecurrent time cannot be deduced by reading TCNT0 only, but the current counting direction of the timer needs to beconsidered as well. This requires servicing interrupts whenever the timer hits TOP (255) and BOTTOM (0) to learnabout each change of the counting direction. For PWM generation, it is usually desired to run it at the highest possiblespeed so filtering the PWM frequency from the modulated output signal is made easy. Thus, the PWM timer runs at fullCPU speed. This causes the overflow and compare match interrupts to be triggered each 256 CPU clocks, so they mustrun with the minimal number of processor cycles possible in order to not impose a too high CPU load by these interruptservice routines. This is the main reason to implement the entire interrupt handling in fine-tuned assembly code ratherthan in C.

In order to verify parts of the algorithm, and the underlying hardware, the demo has been set up in a way so the pin-compatible but more expensive ATtiny45 (or its siblings ATtiny25 and ATtiny85) could be used as well. In that case, noseparate assembly code is required, as two timer channels are avaible.

23.38.1 Hardware setup

The incoming PWM pulse train is fed into PB4. It will generate a pin change interrupt there on eache edge of theincoming signal.

The outgoing PWM is generated through OC0B of timer channel 0 (PB1). For demonstration purposes, a LED shouldbe connected to that pin (like, one of the LEDs of an STK500).

The controllers run on their internal calibrated RC oscillators, 1.2 MHz on the ATtiny13, and 1.0 MHz on the ATtiny45.

23.38.2 A code walkthrough

23.38.2.1 asmdemo.c

After the usual include files, two variables are defined. The first one, pwm_incoming is used to communicate themost recent pulse width detected by the incoming PWM decoder up to the main loop.

The second variable actually only constitutes of a single bit, intbits.pwm_received. This bit will be set wheneverthe incoming PWM decoder has updated pwm_incoming.

Both variables are marked volatile to ensure their readers will always pick up an updated value, as both variables will beset by interrupt service routines.

The function ioinit() initializes the microcontroller peripheral devices. In particular, it starts timer 0 to generate theoutgoing PWM signal on OC0B. Setting OCR0A to 255 (which is the TOP value of timer 0) is used to generate a timer0 overflow A interrupt on the ATtiny13. This interrupt is used to inform the incoming PWM decoder that the countingdirection of channel 0 is just changing from up to down. Likewise, an overflow interrupt will be generated whenever


23.38 Combining C and assembly source files 287

the countdown reached BOTTOM (value 0), where the counter will again alter its counting direction to upwards. Thisinformation is needed in order to know whether the current counter value of TCNT0 is to be evaluated from bottom ortop.

Further, ioinit() activates the pin-change interrupt PCINT0 on any edge of PB4. Finally, PB1 (OC0B) will beactivated as an output pin, and global interrupts are being enabled.

In the ATtiny45 setup, the C code contains an ISR for PCINT0. At each pin-change interrupt, it will first be analyzedwhether the interrupt was caused by a rising or a falling edge. In case of the rising edge, timer 1 will be started with aprescaler of 16 after clearing the current timer value. Then, at the falling edge, the current timer value will be recorded(and timer 1 stopped), the pin-change interrupt will be suspended, and the upper layer will be notified that the incomingPWM measurement data is available.

Function main() first initializes the hardware by calling ioinit(), and then waits until some incoming PWM valueis available. If it is, the output PWM will be adjusted by computing the relative value of the incoming PWM. Finally, thepin-change interrupt is re-enabled, and the CPU is put to sleep.

23.38.2.2 project.h

In order for the interrupt service routines to be as fast as possible, some of the CPU registers are set aside completelyfor use by these routines, so the compiler would not use them for C code. This is arranged for in project.h.

The file is divided into one section that will be used by the assembly source code, and another one to be used by Ccode. The assembly part is distinguished by the preprocessing macro ASSEMBLER (which will be automatically set bythe compiler front-end when preprocessing an assembly-language file), and it contains just macros that give symbolicnames to a number of CPU registers. The preprocessor will then replace the symbolic names by their right-hand sidedefinitions before calling the assembler.

In C code, the compiler needs to see variable declarations for these objects. This is done by using declarations thatbind a variable permanently to a CPU register (see How to permanently bind a variable to a register?). Even in case theC code never has a need to access these variables, declaring the register binding that way causes the compiler to notuse these registers in C code at all.

The flags variable needs to be in the range of r16 through r31 as it is the target of a load immediate (or SER)instruction that is not applicable to the entire register file.

23.38.2.3 isrs.S

This file is a preprocessed assembly source file. The C preprocessor will be run by the compiler front-end first, resolvingall #include, #define etc. directives. The resulting program text will then be passed on to the assembler.

As the C preprocessor strips all C-style comments, preprocessed assembly source files can have both, C-style (/∗... ∗/, // ...) as well as assembly-style (; ...) comments.

At the top, the IO register definition file avr/io.h and the project declaration file project.h are included. Theremainder of the file is conditionally assembled only if the target MCU type is an ATtiny13, so it will be completelyignored for the ATtiny45 option.

Next are the two interrupt service routines for timer 0 compare A match (timer 0 hits TOP, as OCR0A is set to 255) andtimer 0 overflow (timer 0 hits BOTTOM). As discussed above, these are kept as short as possible. They only save SREG(as the flags will be modified by the INC instruction), increment the counter_hi variable which forms the high partof the current time counter (the low part is formed by querying TCNT0 directly), and clear or set the variable flags,respectively, in order to note the current counting direction. The RETI instruction terminates these interrupt serviceroutines. Total cycle count is 8 CPU cycles, so together with the 4 CPU cycles needed for interrupt setup, and the 2cycles for the RJMP from the interrupt vector to the handler, these routines will require 14 out of each 256 CPU cycles,or about 5 % of the overall CPU time.

The pin-change interrupt PCINT0 will be handled in the final part of this file. The basic algorithm is to quickly eval-uate the current system time by fetching the current timer value of TCNT0, and combining it with the overflow partin counter_hi. If the counter is currently counting down rather than up, the value fetched from TCNT0 must be


288 CONTENTS

negated. Finally, if this pin-change interrupt was triggered by a rising edge, the time computed will be recorded as thestart time only. Then, at the falling edge, this start time will be subracted from the current time to compute the actualpulse width seen (left in pwm_incoming), and the upper layers are informed of the new value by setting bit 0 in theintbits flags. At the same time, this pin-change interrupt will be disabled so no new measurement can be performeduntil the upper layer had a chance to process the current value.

23.38.3 The source code

The source code is installed under

$prefix/share/doc/avr-libc/examples/asmdemo/,

where $prefix is a configuration option. For Unix systems, it is usually set to either /usr or /usr/local.


23.39 A simple project 289

23.39 A simple project

At this point, you should have the GNU tools configured, built, and installed on your system. In this chapter, we presenta simple example of using the GNU tools in an AVR project. After reading this chapter, you should have a better feel asto how the tools are used and how a Makefile can be configured.

23.39.1 The Project

This project will use the pulse-width modulator (PWM) to ramp an LED on and off every two seconds. An AT90S2313processor will be used as the controller. The circuit for this demonstration is shown in the schematic diagram. If youhave a development kit, you should be able to use it, rather than build the circuit, for this project.

Note

Meanwhile, the AT90S2313 became obsolete. Either use its successor, the (pin-compatible) ATtiny2313 for theproject, or perhaps the ATmega8 or one of its successors (ATmega48/88/168) which have become quite popularsince the original demo project had been established. For all these more modern devices, it is no longer necessaryto use an external crystal for clocking as they ship with the internal 1 MHz oscillator enabled, so C1, C2, and Q1can be omitted. Normally, for this experiment, the external circuitry on /RESET (R1, C3) can be omitted as well,leaving only the AVR, the LED, the bypass capacitor C4, and perhaps R2. For the ATmega8/48/88/168, use PB1(pin 15 at the DIP-28 package) to connect the LED to. Additionally, this demo has been ported to many differentother AVRs. The location of the respective OC pin varies between different AVRs, and it is mandated by the AVRhardware.

GND

(MOSI)PB5

Q1

4mhz

GND

GND

.1uf

C4

VCC

R1

20K

.01uf

C3

18pf

C2

18pf

C1*

See note [8]

R2LED5MMD1

IC1

1

10

20

5

4

19

18

17

16

15

14

13

12

11

9

8

7

6

3

2

AT90S2313P

(RXD)PD0

(TXD)PD1

(INT0)PD2

(INT1)PD3

(T0)PD4

(T1)PD5

(ICP)PD6

(AIN0)PB0

(AIN1)PB1

PB2

(OCI)PB3

PB4

(MISO)PB6

(SCK)PB7RESET

XTAL2

XTAL1

VCC

GND

Figure 5: Schematic of circuit for demo project

The source code is given in demo.c. For the sake of this example, create a file called demo.c containing this sourcecode. Some of the more important parts of the code are:

Note [1]:

As the AVR microcontroller series has been developed during the past years, new features have been added overtime. Even though the basic concepts of the timer/counter1 are still the same as they used to be back in early 2001when this simple demo was written initially, the names of registers and bits have been changed slightly to reflectthe new features. Also, the port and pin mapping of the output compare match 1A (or 1 for older devices) pin whichis used to control the LED varies between different AVRs. The file iocompat.h tries to abstract between all thisdifferences using some preprocessor #ifdef statements, so the actual program itself can operate on a commonset of symbolic names. The macros defined by that file are:

• OCR the name of the OCR register used to control the PWM (usually either OCR1 or OCR1A)


290 CONTENTS

• DDROC the name of the DDR (data direction register) for the OC output

• OC1 the pin number of the OC1[A] output within its port

• TIMER1_TOP the TOP value of the timer used for the PWM (1023 for 10-bit PWMs, 255 for devices that canonly handle an 8-bit PWM)

• TIMER1_PWM_INIT the initialization bits to be set into control register 1A in order to setup 10-bit (or 8-bit)phase and frequency correct PWM mode

• TIMER1_CLOCKSOURCE the clock bits to set in the respective control register to start the PWM timer; usuallythe timer runs at full CPU clock for 10-bit PWMs, while it runs on a prescaled clock for 8-bit PWMs

Note [2]:

ISR() is a macro that marks the function as an interrupt routine. In this case, the function will get called when timer1 overflows. Setting up interrupts is explained in greater detail in <avr/interrupt.h>: Interrupts.

Note [3]:

The PWM is being used in 10-bit mode, so we need a 16-bit variable to remember the current value.

Note [4]:

This section determines the new value of the PWM.

Note [5]:

Here’s where the newly computed value is loaded into the PWM register. Since we are in an interrupt routine, it is safeto use a 16-bit assignment to the register. Outside of an interrupt, the assignment should only be performed withinterrupts disabled if there’s a chance that an interrupt routine could also access this register (or another registerthat uses TEMP), see the appropriate FAQ entry.

Note [6]:

This routine gets called after a reset. It initializes the PWM and enables interrupts.

Note [7]:

The main loop of the program does nothing – all the work is done by the interrupt routine! The sleep_mode()puts the processor on sleep until the next interrupt, to conserve power. Of course, that probably won’t be noticableas we are still driving a LED, it is merely mentioned here to demonstrate the basic principle.

Note [8]:

Early AVR devices saturate their outputs at rather low currents when sourcing current, so the LED can be connecteddirectly, the resulting current through the LED will be about 15 mA. For modern parts (at least for the ATmega 128),however Atmel has drastically increased the IO source capability, so when operating at 5 V Vcc, R2 is needed. Itsvalue should be about 150 Ohms. When operating the circuit at 3 V, it can still be omitted though.

23.39.2 The Source Code

/** ----------------------------------------------------------------------------

* "THE BEER-WARE LICENSE" (Revision 42):

* <[email protected]> wrote this file. As long as you retain this notice you

* can do whatever you want with this stuff. If we meet some day, and you think

* this stuff is worth it, you can buy me a beer in return. Joerg Wunsch

* ----------------------------------------------------------------------------

*



* Simple AVR demonstration. Controls a LED that can be directly

* connected from OC1/OC1A to GND. The brightness of the LED is

* controlled with the PWM. After each period of the PWM, the PWM

* value is either incremented or decremented, that’s all.

** $Id: demo.c 1637 2008-03-17 21:49:41Z joerg_wunsch $

*/

#include <inttypes.h>#include <avr/io.h>#include <avr/interrupt.h>#include <avr/sleep.h>

#include "iocompat.h" /* Note [1] */

enum { UP, DOWN };

ISR (TIMER1_OVF_vect) /* Note [2] */{

static uint16_t pwm; /* Note [3] */static uint8_t direction;

switch (direction) /* Note [4] */{

case UP:if (++pwm == TIMER1_TOP)

direction = DOWN;break;

case DOWN:if (--pwm == 0)

direction = UP;break;

}

OCR = pwm; /* Note [5] */}

voidioinit (void) /* Note [6] */{

/* Timer 1 is 10-bit PWM (8-bit PWM on some ATtinys). */TCCR1A = TIMER1_PWM_INIT;/** Start timer 1.

** NB: TCCR1A and TCCR1B could actually be the same register, so

* take care to not clobber it.

*/TCCR1B |= TIMER1_CLOCKSOURCE;/** Run any device-dependent timer 1 setup hook if present.

*/#if defined(TIMER1_SETUP_HOOK)

TIMER1_SETUP_HOOK();#endif

/* Set PWM value to 0. */OCR = 0;

/* Enable OC1 as output. */DDROC = _BV (OC1);

/* Enable timer 1 overflow interrupt. */TIMSK = _BV (TOIE1);sei ();

}

intmain (void){

ioinit ();

/* loop forever, the interrupts are doing the rest */

for (;;) /* Note [7] */sleep_mode();

return (0);}


292 CONTENTS

23.39.3 Compiling and Linking

This first thing that needs to be done is compile the source. When compiling, the compiler needs to know the processortype so the -mmcu option is specified. The -Os option will tell the compiler to optimize the code for efficient spaceusage (at the possible expense of code execution speed). The -g is used to embed debug info. The debug info is usefulfor disassemblies and doesn’t end up in the .hex files, so I usually specify it. Finally, the -c tells the compiler to compileand stop – don’t link. This demo is small enough that we could compile and link in one step. However, real-world projectswill have several modules and will typically need to break up the building of the project into several compiles and onelink.

$ avr-gcc -g -Os -mmcu=atmega8 -c demo.c

The compilation will create a demo.o file. Next we link it into a binary called demo.elf.

$ avr-gcc -g -mmcu=atmega8 -o demo.elf demo.o

It is important to specify the MCU type when linking. The compiler uses the -mmcu option to choose start-up filesand run-time libraries that get linked together. If this option isn’t specified, the compiler defaults to the 8515 processorenvironment, which is most certainly what you didn’t want.

23.39.4 Examining the Object File

Now we have a binary file. Can we do anything useful with it (besides put it into the processor?) The GNU Binutils suiteis made up of many useful tools for manipulating object files that get generated. One tool is avr-objdump, whichtakes information from the object file and displays it in many useful ways. Typing the command by itself will cause it tolist out its options.

For instance, to get a feel of the application’s size, the -h option can be used. The output of this option shows howmuch space is used in each of the sections (the .stab and .stabstr sections hold the debugging information and won’tmake it into the ROM file).

An even more useful option is -S. This option disassembles the binary file and intersperses the source code in theoutput! This method is much better, in my opinion, than using the -S with the compiler because this listing includesroutines from the libraries and the vector table contents. Also, all the "fix-ups" have been satisfied. In other words, thelisting generated by this option reflects the actual code that the processor will run.

$ avr-objdump -h -S demo.elf > demo.lst

Here’s the output as saved in the demo.lst file:

demo.elf: file format elf32-avr

Sections:Idx Name Size VMA LMA File off Algn

0 .text 00000110 00000000 00000000 00000094 2**1CONTENTS, ALLOC, LOAD, READONLY, CODE

1 .data 00000000 00800060 00000110 000001a4 2**0CONTENTS, ALLOC, LOAD, DATA

2 .bss 00000003 00800060 00800060 000001a4 2**0ALLOC

3 .stab 00000744 00000000 00000000 000001a4 2**2CONTENTS, READONLY, DEBUGGING

4 .stabstr 00000c4b 00000000 00000000 000008e8 2**0CONTENTS, READONLY, DEBUGGING

5 .comment 00000011 00000000 00000000 00001533 2**0CONTENTS, READONLY



6 .debug_info 0000048c 00000000 00000000 00001544 2**0CONTENTS, READONLY, DEBUGGING

7 .debug_abbrev 0000044e 00000000 00000000 000019d0 2**0CONTENTS, READONLY, DEBUGGING

8 .debug_line 0000001d 00000000 00000000 00001e1e 2**0CONTENTS, READONLY, DEBUGGING

9 .debug_str 0000017a 00000000 00000000 00001e3b 2**0CONTENTS, READONLY, DEBUGGING

Disassembly of section .text:

00000000 <__vectors>:0: 12 c0 rjmp .+36 ; 0x26 <__ctors_end>2: 6d c0 rjmp .+218 ; 0xde <__bad_interrupt>4: 6c c0 rjmp .+216 ; 0xde <__bad_interrupt>6: 6b c0 rjmp .+214 ; 0xde <__bad_interrupt>8: 6a c0 rjmp .+212 ; 0xde <__bad_interrupt>a: 69 c0 rjmp .+210 ; 0xde <__bad_interrupt>c: 68 c0 rjmp .+208 ; 0xde <__bad_interrupt>e: 67 c0 rjmp .+206 ; 0xde <__bad_interrupt>10: 1a c0 rjmp .+52 ; 0x46 <__vector_8>12: 65 c0 rjmp .+202 ; 0xde <__bad_interrupt>14: 64 c0 rjmp .+200 ; 0xde <__bad_interrupt>16: 63 c0 rjmp .+198 ; 0xde <__bad_interrupt>18: 62 c0 rjmp .+196 ; 0xde <__bad_interrupt>1a: 61 c0 rjmp .+194 ; 0xde <__bad_interrupt>1c: 60 c0 rjmp .+192 ; 0xde <__bad_interrupt>1e: 5f c0 rjmp .+190 ; 0xde <__bad_interrupt>20: 5e c0 rjmp .+188 ; 0xde <__bad_interrupt>22: 5d c0 rjmp .+186 ; 0xde <__bad_interrupt>24: 5c c0 rjmp .+184 ; 0xde <__bad_interrupt>

00000026 <__ctors_end>:26: 11 24 eor r1, r128: 1f be out 0x3f, r1 ; 632a: cf e5 ldi r28, 0x5F ; 952c: d4 e0 ldi r29, 0x04 ; 42e: de bf out 0x3e, r29 ; 6230: cd bf out 0x3d, r28 ; 61

00000032 <__do_clear_bss>:32: 10 e0 ldi r17, 0x00 ; 034: a0 e6 ldi r26, 0x60 ; 9636: b0 e0 ldi r27, 0x00 ; 038: 01 c0 rjmp .+2 ; 0x3c <.do_clear_bss_start>

0000003a <.do_clear_bss_loop>:3a: 1d 92 st X+, r1

0000003c <.do_clear_bss_start>:3c: a3 36 cpi r26, 0x63 ; 993e: b1 07 cpc r27, r1740: e1 f7 brne .-8 ; 0x3a <.do_clear_bss_loop>42: 4e d0 rcall .+156 ; 0xe0 <main>44: 61 c0 rjmp .+194 ; 0x108 <exit>

00000046 <__vector_8>:#include "iocompat.h" /* Note [1] */

enum { UP, DOWN };

ISR (TIMER1_OVF_vect) /* Note [2] */{

46: 1f 92 push r148: 0f 92 push r04a: 0f b6 in r0, 0x3f ; 634c: 0f 92 push r04e: 11 24 eor r1, r1


294 CONTENTS

50: 2f 93 push r1852: 8f 93 push r2454: 9f 93 push r25

static uint16_t pwm; /* Note [3] */static uint8_t direction;

switch (direction) /* Note [4] */56: 80 91 62 00 lds r24, 0x00625a: 88 23 and r24, r245c: 01 f1 breq .+64 ; 0x9e <__vector_8+0x58>5e: 81 30 cpi r24, 0x01 ; 160: 81 f4 brne .+32 ; 0x82 <__vector_8+0x3c>

if (++pwm == TIMER1_TOP)direction = DOWN;

break;

case DOWN:if (--pwm == 0)

62: 80 91 60 00 lds r24, 0x006066: 90 91 61 00 lds r25, 0x00616a: 01 97 sbiw r24, 0x01 ; 16c: 90 93 61 00 sts 0x0061, r2570: 80 93 60 00 sts 0x0060, r2474: 00 97 sbiw r24, 0x00 ; 076: 49 f4 brne .+18 ; 0x8a <__vector_8+0x44>

direction = UP;78: 10 92 62 00 sts 0x0062, r17c: 80 e0 ldi r24, 0x00 ; 07e: 90 e0 ldi r25, 0x00 ; 080: 04 c0 rjmp .+8 ; 0x8a <__vector_8+0x44>82: 80 91 60 00 lds r24, 0x006086: 90 91 61 00 lds r25, 0x0061

break;}

OCR = pwm; /* Note [5] */8a: 9b bd out 0x2b, r25 ; 438c: 8a bd out 0x2a, r24 ; 42

}8e: 9f 91 pop r2590: 8f 91 pop r2492: 2f 91 pop r1894: 0f 90 pop r096: 0f be out 0x3f, r0 ; 6398: 0f 90 pop r09a: 1f 90 pop r19c: 18 95 reti

static uint8_t direction;

switch (direction) /* Note [4] */{

case UP:if (++pwm == TIMER1_TOP)

9e: 80 91 60 00 lds r24, 0x0060a2: 90 91 61 00 lds r25, 0x0061a6: 01 96 adiw r24, 0x01 ; 1a8: 90 93 61 00 sts 0x0061, r25ac: 80 93 60 00 sts 0x0060, r24b0: 8f 3f cpi r24, 0xFF ; 255b2: 23 e0 ldi r18, 0x03 ; 3b4: 92 07 cpc r25, r18b6: 49 f7 brne .-46 ; 0x8a <__vector_8+0x44>

direction = DOWN;b8: 81 e0 ldi r24, 0x01 ; 1ba: 80 93 62 00 sts 0x0062, r24be: 8f ef ldi r24, 0xFF ; 255c0: 93 e0 ldi r25, 0x03 ; 3c2: e3 cf rjmp .-58 ; 0x8a <__vector_8+0x44>



000000c4 <ioinit>:


/* Timer 1 is 10-bit PWM (8-bit PWM on some ATtinys). */TCCR1A = TIMER1_PWM_INIT;

c4: 83 e8 ldi r24, 0x83 ; 131c6: 8f bd out 0x2f, r24 ; 47

* Start timer 1.



*/TCCR1B |= TIMER1_CLOCKSOURCE;

c8: 8e b5 in r24, 0x2e ; 46ca: 81 60 ori r24, 0x01 ; 1cc: 8e bd out 0x2e, r24 ; 46

#if defined(TIMER1_SETUP_HOOK)TIMER1_SETUP_HOOK();

#endif


ce: 1b bc out 0x2b, r1 ; 43d0: 1a bc out 0x2a, r1 ; 42


d2: 82 e0 ldi r24, 0x02 ; 2d4: 87 bb out 0x17, r24 ; 23

/* Enable timer 1 overflow interrupt. */TIMSK = _BV (TOIE1);

d6: 84 e0 ldi r24, 0x04 ; 4d8: 89 bf out 0x39, r24 ; 57

sei ();da: 78 94 seidc: 08 95 ret

000000de <__bad_interrupt>:de: 90 cf rjmp .-224 ; 0x0 <__vectors>

000000e0 <main>:


/* Timer 1 is 10-bit PWM (8-bit PWM on some ATtinys). */TCCR1A = TIMER1_PWM_INIT;

e0: 83 e8 ldi r24, 0x83 ; 131e2: 8f bd out 0x2f, r24 ; 47

* Start timer 1.



*/TCCR1B |= TIMER1_CLOCKSOURCE;

e4: 8e b5 in r24, 0x2e ; 46e6: 81 60 ori r24, 0x01 ; 1e8: 8e bd out 0x2e, r24 ; 46

#if defined(TIMER1_SETUP_HOOK)TIMER1_SETUP_HOOK();

#endif



296 CONTENTS

ea: 1b bc out 0x2b, r1 ; 43ec: 1a bc out 0x2a, r1 ; 42


ee: 82 e0 ldi r24, 0x02 ; 2f0: 87 bb out 0x17, r24 ; 23

/* Enable timer 1 overflow interrupt. */TIMSK = _BV (TOIE1);

f2: 84 e0 ldi r24, 0x04 ; 4f4: 89 bf out 0x39, r24 ; 57

sei ();f6: 78 94 sei

ioinit ();

/* loop forever, the interrupts are doing the rest */

for (;;) /* Note [7] */sleep_mode();

f8: 85 b7 in r24, 0x35 ; 53fa: 80 68 ori r24, 0x80 ; 128fc: 85 bf out 0x35, r24 ; 53fe: 88 95 sleep100: 85 b7 in r24, 0x35 ; 53102: 8f 77 andi r24, 0x7F ; 127104: 85 bf out 0x35, r24 ; 53106: f8 cf rjmp .-16 ; 0xf8 <main+0x18>

00000108 <exit>:108: f8 94 cli10a: 00 c0 rjmp .+0 ; 0x10c <_exit>

0000010c <_exit>:10c: f8 94 cli

0000010e <__stop_program>:10e: ff cf rjmp .-2 ; 0x10e <__stop_program>

23.39.5 Linker Map Files

avr-objdump is very useful, but sometimes it’s necessary to see information about the link that can only be generatedby the linker. A map file contains this information. A map file is useful for monitoring the sizes of your code and data.It also shows where modules are loaded and which modules were loaded from libraries. It is yet another view of yourapplication. To get a map file, I usually add -Wl,-Map,demo.map to my link command. Relink the application usingthe following command to generate demo.map (a portion of which is shown below).

$ avr-gcc -g -mmcu=atmega8 -Wl,-Map,demo.map -o demo.elf demo.o

Some points of interest in the demo.map file are:

.rela.plt

*(.rela.plt)

.text 0x0000000000000000 0x110

*(.vectors).vectors 0x0000000000000000 0x26 /tmp/avr-libc-1_8_1-release/avr/lib/avr4/atmega8/crtm8.o

0x0000000000000000 __vectors0x0000000000000000 __vector_default

*(.vectors)

*(.progmem.gcc*)0x0000000000000026 . = ALIGN (0x2)0x0000000000000026 __trampolines_start = .

*(.trampolines).trampolines 0x0000000000000026 0x0 linker stubs

*(.trampolines*)



0x0000000000000026 __trampolines_end = .

*(.progmem*)0x0000000000000026 . = ALIGN (0x2)

*(.jumptables)

*(.jumptables*)

*(.lowtext)

*(.lowtext*)0x0000000000000026 __ctors_start = .

The .text segment (where program instructions are stored) starts at location 0x0.

*(.fini2)

*(.fini2)

*(.fini1)

*(.fini1)

*(.fini0).fini0 0x000000000000010c 0x4 /usr/local/lib/gcc/avr/4.8.3/avr4/libgcc.a(_exit.o)

*(.fini0)0x0000000000000110 _etext = .

.data 0x0000000000800060 0x0 load address 0x00000000000001100x0000000000800060 PROVIDE (__data_start, .)

*(.data).data 0x0000000000800060 0x0 demo.o.data 0x0000000000800060 0x0 /tmp/avr-libc-1_8_1-release/avr/lib/avr4/atmega8/crtm8.o.data 0x0000000000800060 0x0 /tmp/avr-libc-1_8_1-release/avr/lib/avr4/

exit.o.data 0x0000000000800060 0x0 /usr/local/lib/gcc/avr/4.8.3/avr4/libgcc.a(_exit.o).data 0x0000000000800060 0x0 /usr/local/lib/gcc/avr/4.8.3/avr4/libgcc.a(_clear_bss.o)

*(.data*)

*(.rodata)

*(.rodata*)

*(.gnu.linkonce.d*)0x0000000000800060 . = ALIGN (0x2)0x0000000000800060 _edata = .0x0000000000800060 PROVIDE (__data_end, .)

.bss 0x0000000000800060 0x30x0000000000800060 PROVIDE (__bss_start, .)

*(.bss).bss 0x0000000000800060 0x3 demo.o.bss 0x0000000000800063 0x0 /tmp/avr-libc-1_8_1-release/avr/lib/avr4/atmega8/crtm8.o.bss 0x0000000000800063 0x0 /tmp/avr-libc-1_8_1-release/avr/lib/avr4/

exit.o.bss 0x0000000000800063 0x0 /usr/local/lib/gcc/avr/4.8.3/avr4/libgcc.a(_exit.o).bss 0x0000000000800063 0x0 /usr/local/lib/gcc/avr/4.8.3/avr4/libgcc.a(_clear_bss.o)

*(.bss*)

*(COMMON)0x0000000000800063 PROVIDE (__bss_end, .)0x0000000000000110 __data_load_start = LOADADDR (.data)0x0000000000000110 __data_load_end = (__data_load_start + SIZEOF (.data))

.noinit 0x0000000000800063 0x00x0000000000800063 PROVIDE (__noinit_start, .)

*(.noinit*)0x0000000000800063 PROVIDE (__noinit_end, .)0x0000000000800063 _end = .0x0000000000800063 PROVIDE (__heap_start, .)

.eeprom 0x0000000000810000 0x0

*(.eeprom*)0x0000000000810000 __eeprom_end = .

The last address in the .text segment is location 0x114 ( denoted by _etext ), so the instructions use up 276 bytesof FLASH.

The .data segment (where initialized static variables are stored) starts at location 0x60, which is the first address afterthe register bank on an ATmega8 processor.

The next available address in the .data segment is also location 0x60, so the application has no initialized data.

The .bss segment (where uninitialized data is stored) starts at location 0x60.

The next available address in the .bss segment is location 0x63, so the application uses 3 bytes of uninitialized data.


298 CONTENTS

The .eeprom segment (where EEPROM variables are stored) starts at location 0x0.

The next available address in the .eeprom segment is also location 0x0, so there aren’t any EEPROM variables.

23.39.6 Generating Intel Hex Files

We have a binary of the application, but how do we get it into the processor? Most (if not all) programmers will notaccept a GNU executable as an input file, so we need to do a little more processing. The next step is to extract portionsof the binary and save the information into .hex files. The GNU utility that does this is called avr-objcopy.

The ROM contents can be pulled from our project’s binary and put into the file demo.hex using the following command:

$ avr-objcopy -j .text -j .data -O ihex demo.elf demo.hex

The resulting demo.hex file contains:

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

The -j option indicates that we want the information from the .text and .data segment extracted. If we specify theEEPROM segment, we can generate a .hex file that can be used to program the EEPROM:

$ avr-objcopy -j .eeprom --change-section-lma .eeprom=0 -O ihex demo.elf demo_eeprom.hex

There is no demo_eeprom.hex file written, as that file would be empty.

Starting with version 2.17 of the GNU binutils, the avr-objcopy command that used to generate the empty EEPROMfiles now aborts because of the empty input section .eeprom, so these empty files are not generated. It also signals anerror to the Makefile which will be caught there, and makes it print a message about the empty file not being generated.

23.39.7 Letting Make Build the Project

Rather than type these commands over and over, they can all be placed in a make file. To build the demo project usingmake, save the following in a file called Makefile.

Note

This Makefile can only be used as input for the GNU version of make.

PRG = demoOBJ = demo.o#MCU_TARGET = at90s2313



#MCU_TARGET = at90s2333#MCU_TARGET = at90s4414#MCU_TARGET = at90s4433#MCU_TARGET = at90s4434#MCU_TARGET = at90s8515#MCU_TARGET = at90s8535#MCU_TARGET = atmega128#MCU_TARGET = atmega1280#MCU_TARGET = atmega1281#MCU_TARGET = atmega1284p#MCU_TARGET = atmega16#MCU_TARGET = atmega163#MCU_TARGET = atmega164p#MCU_TARGET = atmega165#MCU_TARGET = atmega165p#MCU_TARGET = atmega168#MCU_TARGET = atmega169#MCU_TARGET = atmega169p#MCU_TARGET = atmega2560#MCU_TARGET = atmega2561#MCU_TARGET = atmega32#MCU_TARGET = atmega324p#MCU_TARGET = atmega325#MCU_TARGET = atmega3250#MCU_TARGET = atmega329#MCU_TARGET = atmega3290#MCU_TARGET = atmega32u4#MCU_TARGET = atmega48#MCU_TARGET = atmega64#MCU_TARGET = atmega640#MCU_TARGET = atmega644#MCU_TARGET = atmega644p#MCU_TARGET = atmega645#MCU_TARGET = atmega6450#MCU_TARGET = atmega649#MCU_TARGET = atmega6490MCU_TARGET = atmega8#MCU_TARGET = atmega8515#MCU_TARGET = atmega8535#MCU_TARGET = atmega88#MCU_TARGET = attiny2313#MCU_TARGET = attiny24#MCU_TARGET = attiny25#MCU_TARGET = attiny26#MCU_TARGET = attiny261#MCU_TARGET = attiny44#MCU_TARGET = attiny45#MCU_TARGET = attiny461#MCU_TARGET = attiny84#MCU_TARGET = attiny85#MCU_TARGET = attiny861OPTIMIZE = -O2

DEFS =LIBS =

# You should not have to change anything below here.

CC = avr-gcc

# Override is only needed by avr-lib build system.

override CFLAGS = -g -Wall $(OPTIMIZE) -mmcu=$(MCU_TARGET) $(DEFS)override LDFLAGS = -Wl,-Map,$(PRG).map

OBJCOPY = avr-objcopyOBJDUMP = avr-objdump

all: $(PRG).elf lst text eeprom

$(PRG).elf: $(OBJ)$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^ $(LIBS)

# dependency:demo.o: demo.c iocompat.h

clean:rm -rf *.o $(PRG).elf *.eps *.png *.pdf *.bakrm -rf *.lst *.map $(EXTRA_CLEAN_FILES)

lst: $(PRG).lst


300 CONTENTS

%.lst: %.elf$(OBJDUMP) -h -S $< > $@

# Rules for building the .text rom images

text: hex bin srec

hex: $(PRG).hexbin: $(PRG).binsrec: $(PRG).srec

%.hex: %.elf$(OBJCOPY) -j .text -j .data -O ihex $< $@

%.srec: %.elf$(OBJCOPY) -j .text -j .data -O srec $< $@

%.bin: %.elf$(OBJCOPY) -j .text -j .data -O binary $< $@

# Rules for building the .eeprom rom images

eeprom: ehex ebin esrec

ehex: $(PRG)_eeprom.hexebin: $(PRG)_eeprom.binesrec: $(PRG)_eeprom.srec

%_eeprom.hex: %.elf$(OBJCOPY) -j .eeprom --change-section-lma .eeprom=0 -O ihex $< $@ \|| { echo empty $@ not generated; exit 0; }

%_eeprom.srec: %.elf$(OBJCOPY) -j .eeprom --change-section-lma .eeprom=0 -O srec $< $@ \|| { echo empty $@ not generated; exit 0; }

%_eeprom.bin: %.elf$(OBJCOPY) -j .eeprom --change-section-lma .eeprom=0 -O binary $< $@ \|| { echo empty $@ not generated; exit 0; }

# Every thing below here is used by avr-libc’s build system and can be ignored# by the casual user.

FIG2DEV = fig2devEXTRA_CLEAN_FILES = *.hex *.bin *.srec

dox: eps png pdf

eps: $(PRG).epspng: $(PRG).pngpdf: $(PRG).pdf

%.eps: %.fig$(FIG2DEV) -L eps $< $@

%.pdf: %.fig$(FIG2DEV) -L pdf $< $@

%.png: %.fig$(FIG2DEV) -L png $< $@

23.39.8 Reference to the source code


$prefix/share/doc/avr-libc/examples/demo/,



23.40 A more sophisticated project 301

23.40 A more sophisticated project

This project extends the basic idea of the simple project to control a LED with a PWM output, but adds methods to adjustthe LED brightness. It employs a lot of the basic concepts of avr-libc to achieve that goal.

Understanding this project assumes the simple project has been understood in full, as well as being acquainted with thebasic hardware concepts of an AVR microcontroller.


The demo is set up in a way so it can be run on the ATmega16 that ships with the STK500 development kit. The onlyexternal part needed is a potentiometer attached to the ADC. It is connected to a 10-pin ribbon cable for port A, bothends of the potentiometer to pins 9 (GND) and 10 (VCC), and the wiper to pin 1 (port A0). A bypass capacitor from pin1 to pin 9 (like 47 nF) is recommendable.

Figure 6: Setup of the STK500

The coloured patch cables are used to provide various interconnections. As there are only four of them in the ST←↩K500, there are two options to connect them for this demo. The second option for the yellow-green cable is shown inparenthesis in the table. Alternatively, the "squid" cable from the JTAG ICE kit can be used if available.

Port Header Color Function Connect toD0 1 brown RxD RXD of the RS-232

headerD1 2 grey TxD TXD of the RS-232

header


302 CONTENTS

D2 3 black button "down" SW0 (pin 1 switchesheader)

D3 4 red button "up" SW1 (pin 2 switchesheader)

D4 5 green button "ADC" SW2 (pin 3 switchesheader)

D5 6 blue LED LED0 (pin 1 LEDsheader)

D6 7 (green) clock out LED1 (pin 2 LEDsheader)

D7 8 white 1-second flash LED2 (pin 3 LEDsheader)

GND 9 unusedVCC 10 unused

Figure 7: Wiring of the STK500

The following picture shows the alternate wiring where LED1 is connected but SW2 is not:



Figure 8: Wiring option #2 of the STK500

As an alternative, this demo can also be run on the popular ATmega8 controller, or its successor ATmega88 as well asthe ATmega48 and ATmega168 variants of the latter. These controllers do not have a port named "A", so their ADCinputs are located on port C instead, thus the potentiometer needs to be attached to port C. Likewise, the OC1A outputis not on port D pin 5 but on port B pin 1 (PB1). Thus, the above cabling scheme needs to be changed so that PB1connects to the LED0 pin. (PD6 remains unconnected.) When using the STK500, use one of the jumper cables for thisconnection. All other port D pins should be connected the same way as described for the ATmega16 above.

When not using an STK500 starter kit, attach the LEDs through some resistor to Vcc (low-active LEDs), and attachpushbuttons from the respective input pins to GND. The internal pull-up resistors are enabled for the pushbutton pins,so no external resistors are needed.

Finally, the demo has been ported to the ATtiny2313 as well. As this AVR does not offer an ADC, everything related tohandling the ADC is disabled in the code for that MCU type. Also, port D of this controller type only features 6 pins, sothe 1-second flash LED had to be moved from PD6 to PD4. (PD4 is used as the ADC control button on the other MCUtypes, but that is not needed here.) OC1A is located at PB3 on this device.

The MCU_TARGET macro in the Makefile needs to be adjusted appropriately for the alternative controller types.

The flash ROM and RAM consumption of this demo are way below the resources of even an ATmega48, and still wellwithin the capabilities of an ATtiny2313. The major advantage of experimenting with the ATmega16 (in addition that itships together with an STK500 anyway) is that it can be debugged online via JTAG. Likewise, the ATmega48/88/168and ATtiny2313 devices can be debugged through debugWire, using the Atmel JTAG ICE mkII or the low-cost AVRDragon.

Note that in the explanation below, all port/pin names are applicable to the ATmega16 setup.

23.40.2 Functional overview

PD6 will be toggled with each internal clock tick (approx. 10 ms). PD7 will flash once per second.

PD0 and PD1 are configured as UART IO, and can be used to connect the demo kit to a PC (9600 Bd, 8N1 frameformat). The demo application talks to the serial port, and it can be controlled from the serial port.

PD2 through PD4 are configured as inputs, and control the application unless control has been taken over by the serialport. Shorting PD2 to GND will decrease the current PWM value, shorting PD3 to GND will increase it.

While PD4 is shorted to GND, one ADC conversion for channel 0 (ADC input is on PA0) will be triggered each internalclock tick, and the resulting value will be used as the PWM value. So the brightness of the LED follows the analog input


304 CONTENTS

value on PC0. VAREF on the STK500 should be set to the same value as VCC.

When running in serial control mode, the function of the watchdog timer can be demonstrated by typing an ‘r’. This willmake the demo application run in a tight loop without retriggering the watchdog so after some seconds, the watchdogwill reset the MCU. This situation can be figured out on startup by reading the MCUCSR register.

The current value of the PWM is backed up in an EEPROM cell after about 3 seconds of idle time after the last change.If that EEPROM cell contains a reasonable (i. e. non-erased) value at startup, it is taken as the initial value for the PWM.This virtually preserves the last value across power cycles. By not updating the EEPROM immmediately but only aftera timeout, EEPROM wear is reduced considerably compared to immediately writing the value at each change.


This section explains the ideas behind individual parts of the code. The source code has been divided into numberedparts, and the following subsections explain each of these parts.

23.40.3.1 Part 1: Macro definitions

A number of preprocessor macros are defined to improve readability and/or portability of the application.

The first macros describe the IO pins our LEDs and pushbuttons are connected to. This provides some kind of mini-HAL(hardware abstraction layer) so should some of the connections be changed, they don’t need to be changed inside thecode but only on top. Note that the location of the PWM output itself is mandated by the hardware, so it cannot beeasily changed. As the ATmega48/88/168 controllers belong to a more recent generation of AVRs, a number of registerand bit names have been changed there, so they are mapped back to their ATmega8/16 equivalents to keep the actualprogram code portable.

The name F_CPU is the conventional name to describe the CPU clock frequency of the controller. This demo project justuses the internal calibrated 1 MHz RC oscillator that is enabled by default. Note that when using the <util/delay.←↩h> functions, F_CPU needs to be defined before including that file.

The remaining macros have their own comments in the source code. The macro TMR1_SCALE shows how to use thepreprocessor and the compiler’s constant expression computation to calculate the value of timer 1’s post-scaler in away so it only depends on F_CPU and the desired software clock frequency. While the formula looks a bit complicated,using a macro offers the advantage that the application will automatically scale to new target softclock or master CPUfrequencies without having to manually re-calculate hardcoded constants.

23.40.3.2 Part 2: Variable definitions

The intflags structure demonstrates a way to allocate bit variables in memory. Each of the interrupt service routinesjust sets one bit within that structure, and the application’s main loop then monitors the bits in order to act appropriately.

Like all variables that are used to communicate values between an interrupt service routine and the main application, itis declared volatile.

The variable ee_pwm is not a variable in the classical C sense that could be used as an lvalue or within an expressionto obtain its value. Instead, the

__attribute__((section(".eeprom")))

marks it as belonging to the EEPROM section. This section is merely used as a placeholder so the compiler canarrange for each individual variable’s location in EEPROM. The compiler will also keep track of initial values assigned,and usually the Makefile is arranged to extract these initial values into a separate load file (largedemo_eeprom.∗ inthis case) that can be used to initialize the EEPROM.

The actual EEPROM IO must be performed manually.

Similarly, the variable mcucsr is kept in the .noinit section in order to prevent it from being cleared upon applicationstartup.



23.40.3.3 Part 3: Interrupt service routines

The ISR to handle timer 1’s overflow interrupt arranges for the software clock. While timer 1 runs the PWM, it calls itsoverflow handler rather frequently, so the TMR1_SCALE value is used as a postscaler to reduce the internal softwareclock frequency further. If the software clock triggers, it sets the tmr_int bitfield, and defers all further tasks to themain loop.

The ADC ISR just fetches the value from the ADC conversion, disables the ADC interrupt again, and announces thepresence of the new value in the adc_int bitfield. The interrupt is kept disabled while not needed, because the ADCwill also be triggered by executing the SLEEP instruction in idle mode (which is the default sleep mode). Another optionwould be to turn off the ADC completely here, but that increases the ADC’s startup time (not that it would matter muchfor this application).

23.40.3.4 Part 4: Auxiliary functions

The function handle_mcucsr() uses two attribute declarators to achieve specific goals. First, it will instructthe compiler to place the generated code into the .init3 section of the output. Thus, it will become part of the applicationinitialization sequence. This is done in order to fetch (and clear) the reason of the last hardware reset from MCUCSR asearly as possible. There is a short period of time where the next reset could already trigger before the current reasonhas been evaluated. This also explains why the variable mcucsr that mirrors the register’s value needs to be placedinto the .noinit section, because otherwise the default initialization (which happens after .init3) would blank the valueagain.

As the initialization code is not called using CALL/RET instructions but rather concatenated together, the compiler needsto be instructed to omit the entire function prologue and epilogue. This is performed by the naked attribute. So whilesyntactically, handle_mcucsr() is a function to the compiler, the compiler will just emit the instructions for it withoutsetting up any stack frame, and not even a RET instruction at the end.

Function ioinit() centralizes all hardware setup. The very last part of that function demonstrates the use of theEEPROM variable ee_pwm to obtain an EEPROM address that can in turn be applied as an argument to eeprom_←↩read_word().

The following functions handle UART character and string output. (UART input is handled by an ISR.) There aretwo string output functions, printstr() and printstr_p(). The latter function fetches the string from programmemory. Both functions translate a newline character into a carriage return/newline sequence, so a simple \n can beused in the source code.

The function set_pwm() propagates the new PWM value to the PWM, performing range checking. When the valuehas been changed, the new percentage will be announced on the serial link. The current value is mirrored in the variablepwm so others can use it in calculations. In order to allow for a simple calculation of a percentage value without requiringfloating-point mathematics, the maximal value of the PWM is restricted to 1000 rather than 1023, so a simple divisionby 10 can be used. Due to the nature of the human eye, the difference in LED brightness between 1000 and 1023 is notnoticable anyway.

23.40.3.5 Part 5: main()

At the start of main(), a variable mode is declared to keep the current mode of operation. An enumeration is used toimprove the readability. By default, the compiler would allocate a variable of type int for an enumeration. The packedattribute declarator instructs the compiler to use the smallest possible integer type (which would be an 8-bit type here).

After some initialization actions, the application’s main loop follows. In an embedded application, this is normally aninfinite loop as there is nothing an application could "exit" into anyway.

At the beginning of the loop, the watchdog timer will be retriggered. If that timer is not triggered for about 2 seconds, itwill issue a hardware reset. Care needs to be taken that no code path blocks longer than this, or it needs to frequentlyperform watchdog resets of its own. An example of such a code path would be the string IO functions: for an overlylarge string to print (about 2000 characters at 9600 Bd), they might block for too long.

The loop itself then acts on the interrupt indication bitfields as appropriate, and will eventually put the CPU on sleep at


306 CONTENTS

its end to conserve power.

The first interrupt bit that is handled is the (software) timer, at a frequency of approximately 100 Hz. The CLOCKOUTpin will be toggled here, so e. g. an oscilloscope can be used on that pin to measure the accuracy of our softwareclock. Then, the LED flasher for LED2 ("We are alive"-LED) is built. It will flash that LED for about 50 ms, and pauseit for another 950 ms. Various actions depending on the operation mode follow. Finally, the 3-second backup timer isimplemented that will write the PWM value back to EEPROM once it is not changing anymore.

The ADC interrupt will just adjust the PWM value only.

Finally, the UART Rx interrupt will dispatch on the last character received from the UART.

All the string literals that are used as informational messages within main() are placed in program memory so noSRAM needs to be allocated for them. This is done by using the PSTR macro, and passing the string to printstr←↩_p().



$prefix/share/doc/avr-libc/examples/largedemo/largedemo.c,



23.41 Using the standard IO facilities 307

23.41 Using the standard IO facilities

This project illustrates how to use the standard IO facilities (stdio) provided by this library. It assumes a basic knowledgeof how the stdio subsystem is used in standard C applications, and concentrates on the differences in this library’s imple-mentation that mainly result from the differences of the microcontroller environment, compared to a hosted environmentof a standard computer.

This demo is meant to supplement the documentation, not to replace it.


The demo is set up in a way so it can be run on the ATmega16 that ships with the STK500 development kit. The UARTport needs to be connected to the RS-232 "spare" port by a jumper cable that connects PD0 to RxD and PD1 to TxD.The RS-232 channel is set up as standard input (stdin) and standard output (stdout), respectively.

In order to have a different device available for a standard error channel (stderr), an industry-standard LCD displaywith an HD44780-compatible LCD controller has been chosen. This display needs to be connected to port A of theSTK500 in the following way:

Port Header FunctionA0 1 LCD D4A1 2 LCD D5A2 3 LCD D6A3 4 LCD D7A4 5 LCD R/∼WA5 6 LCD EA6 7 LCD RSA7 8 unusedGND 9 GNDVCC 10 Vcc

Figure 9: Wiring of the STK500

The LCD controller is used in 4-bit mode, including polling the "busy" flag so the R/∼W line from the LCD controllerneeds to be connected. Note that the LCD controller has yet another supply pin that is used to adjust the LCD’s contrast(V5). Typically, that pin connects to a potentiometer between Vcc and GND. Often, it might work to just connect that pinto GND, while leaving it unconnected usually yields an unreadable display.


308 CONTENTS

Port A has been chosen as 7 pins are needed to connect the LCD, yet all other ports are already partially in use: port Bhas the pins for in-system programming (ISP), port C has the ports for JTAG (can be used for debugging), and port D isused for the UART connection.

23.41.2 Functional overview

The project consists of the following files:

• stdiodemo.c This is the main example file.

• defines.h Contains some global defines, like the LCD wiring

• hd44780.c Implementation of an HD44780 LCD display driver

• hd44780.h Interface declarations for the HD44780 driver

• lcd.c Implementation of LCD character IO on top of the HD44780 driver

• lcd.h Interface declarations for the LCD driver

• uart.c Implementation of a character IO driver for the internal UART

• uart.h Interface declarations for the UART driver


23.41.3.1 stdiodemo.c

As usual, include files go first. While conventionally, system header files (those in angular brackets < ... >) go beforeapplication-specific header files (in double quotes), defines.h comes as the first header file here. The main reasonis that this file defines the value of F_CPU which needs to be known before including <utils/delay.h>.

The function ioinit() summarizes all hardware initialization tasks. As this function is declared to be module-internalonly (static), the compiler will notice its simplicity, and with a reasonable optimization level in effect, it will inlinethat function. That needs to be kept in mind when debugging, because the inlining might cause the debugger to "jumparound wildly" at a first glance when single-stepping.

The definitions of uart_str and lcd_str set up two stdio streams. The initialization is done using the FDEV_SET←↩UP_STREAM() initializer template macro, so a static object can be constructed that can be used for IO purposes. Thisinitializer macro takes three arguments, two function macros to connect the corresponding output and input functions,respectively, the third one describes the intent of the stream (read, write, or both). Those functions that are not requiredby the specified intent (like the input function for lcd_str which is specified to only perform output operations) can begiven as NULL.

The stream uart_str corresponds to input and output operations performed over the RS-232 connection to a terminal(e.g. from/to a PC running a terminal program), while the lcd_str stream provides a method to display character dataon the LCD text display.

The function delay_1s() suspends program execution for approximately one second. This is done using the _←↩delay_ms() function from <util/delay.h> which in turn needs the F_CPU macro in order to adjust the cyclecounts. As the _delay_ms() function has a limited range of allowable argument values (depending on F_CPU), avalue of 10 ms has been chosen as the base delay which would be safe for CPU frequencies of up to about 26 MHz.This function is then called 100 times to accomodate for the actual one-second delay.

In a practical application, long delays like this one were better be handled by a hardware timer, so the main CPU wouldbe free for other tasks while waiting, or could be put on sleep.

At the beginning of main(), after initializing the peripheral devices, the default stdio streams stdin, stdout, andstderr are set up by using the existing static FILE stream objects. While this is not mandatory, the availability of



stdin and stdout allows to use the shorthand functions (e.g. printf() instead of fprintf()), and stderrcan mnemonically be referred to when sending out diagnostic messages.

Just for demonstration purposes, stdin and stdout are connected to a stream that will perform UART IO, whilestderr is arranged to output its data to the LCD text display.

Finally, a main loop follows that accepts simple "commands" entered via the RS-232 connection, and performs a fewsimple actions based on the commands.

First, a prompt is sent out using printf_P() (which takes a program space string). The string is read into an internalbuffer as one line of input, using fgets(). While it would be also possible to use gets() (which implicitly reads fromstdin), gets() has no control that the user’s input does not overflow the input buffer provided so it should never beused at all.

If fgets() fails to read anything, the main loop is left. Of course, normally the main loop of a microcontroller applicationis supposed to never finish, but again, for demonstrational purposes, this explains the error handling of stdio. fgets()will return NULL in case of an input error or end-of-file condition on input. Both these conditions are in the domain ofthe function that is used to establish the stream, uart_putchar() in this case. In short, this function returns EOFin case of a serial line "break" condition (extended start condition) has been recognized on the serial line. Common PCterminal programs allow to assert this condition as some kind of out-of-band signalling on an RS-232 connection.

When leaving the main loop, a goodbye message is sent to standard error output (i.e. to the LCD), followed by threedots in one-second spacing, followed by a sequence that will clear the LCD. Finally, main() will be terminated, and thelibrary will add an infinite loop, so only a CPU reset will be able to restart the application.

There are three "commands" recognized, each determined by the first letter of the line entered (converted to lowercase):

• The ’q’ (quit) command has the same effect of leaving the main loop.

• The ’l’ (LCD) command takes its second argument, and sends it to the LCD.

• The ’u’ (UART) command takes its second argument, and sends it back to the UART connection.

Command recognition is done using sscanf() where the first format in the format string just skips over the commanditself (as the assignment suppression modifier ∗ is given).

23.41.3.2 defines.h

This file just contains a few peripheral definitions.

The F_CPU macro defines the CPU clock frequency, to be used in delay loops, as well as in the UART baud ratecalculation.

The macro UART_BAUD defines the RS-232 baud rate. Depending on the actual CPU frequency, only a limited rangeof baud rates can be supported.

The remaining macros customize the IO port and pins used for the HD44780 LCD driver. Each definition consists of aletter naming the port this pin is attached to, and a respective bit number. For accessing the data lines, only the firstdata line gets its own macro (line D4 on the HD44780, lines D0 through D3 are not used in 4-bit mode), all other datalines are expected to be in ascending order next to D4.

23.41.3.3 hd44780.h

This file describes the public interface of the low-level LCD driver that interfaces to the HD44780 LCD controller. Publicfunctions are available to initialize the controller into 4-bit mode, to wait for the controller’s busy bit to be clear, and toread or write one byte from or to the controller.

As there are two different forms of controller IO, one to send a command or receive the controller status (RS signalclear), and one to send or receive data to/from the controller’s SRAM (RS asserted), macros are provided that build onthe mentioned function primitives.


310 CONTENTS

Finally, macros are provided for all the controller commands to allow them to be used symbolically. The HD44780datasheet explains these basic functions of the controller in more detail.

23.41.3.4 hd44780.c

This is the implementation of the low-level HD44780 LCD controller driver.

On top, a few preprocessor glueing tricks are used to establish symbolic access to the hardware port pins the LCDcontroller is attached to, based on the application’s definitions made in defines.h.

The hd44780_pulse_e() function asserts a short pulse to the controller’s E (enable) pin. Since reading back thedata asserted by the LCD controller needs to be performed while E is active, this function reads and returns the inputdata if the parameter readback is true. When called with a compile-time constant parameter that is false, the compilerwill completely eliminate the unused readback operation, as well as the return value as part of its optimizations.

As the controller is used in 4-bit interface mode, all byte IO to/from the controller needs to be handled as two nibble IOs.The functions hd44780_outnibble() and hd44780_innibble() implement this. They do not belong to thepublic interface, so they are declared static.

Building upon these, the public functions hd44780_outbyte() and hd44780_inbyte() transfer one byteto/from the controller.

The function hd44780_wait_ready() waits for the controller to become ready, by continuously polling the con-troller’s status (which is read by performing a byte read with the RS signal cleard), and examining the BUSY flag withinthe status byte. This function needs to be called before performing any controller IO.

Finally, hd44780_init() initializes the LCD controller into 4-bit mode, based on the initialization sequence mandatedby the datasheet. As the BUSY flag cannot be examined yet at this point, this is the only part of this code where timeddelays are used. While the controller can perform a power-on reset when certain constraints on the power supply risetime are met, always calling the software initialization routine at startup ensures the controller will be in a known state.This function also puts the interface into 4-bit mode (which would not be done automatically after a power-on reset).

23.41.3.5 lcd.h

This function declares the public interface of the higher-level (character IO) LCD driver.

23.41.3.6 lcd.c

The implementation of the higher-level LCD driver. This driver builds on top of the HD44780 low-level LCD controllerdriver, and offers a character IO interface suitable for direct use by the standard IO facilities. Where the low-level H←↩D44780 driver deals with setting up controller SRAM addresses, writing data to the controller’s SRAM, and controllingdisplay functions like clearing the display, or moving the cursor, this high-level driver allows to just write a character tothe LCD, in the assumption this will somehow show up on the display.

Control characters can be handled at this level, and used to perform specific actions on the LCD. Currently, there is onlyone control character that is being dealt with: a newline character (\n) is taken as an indication to clear the displayand set the cursor into its initial position upon reception of the next character, so a "new line" of text can be displayed.Therefore, a received newline character is remembered until more characters have been sent by the application, andwill only then cause the display to be cleared before continuing. This provides a convenient abstraction where full linesof text can be sent to the driver, and will remain visible at the LCD until the next line is to be displayed.

Further control characters could be implemented, e. g. using a set of escape sequences. That way, it would be possibleto implement self-scrolling display lines etc.

The public function lcd_init() first calls the initialization entry point of the lower-level HD44780 driver, and thensets up the LCD in a way we’d like to (display cleared, non-blinking cursor enabled, SRAM addresses are increasing socharacters will be written left to right).

The public function lcd_putchar() takes arguments that make it suitable for being passed as a put() functionpointer to the stdio stream initialization functions and macros (fdevopen(), FDEV_SETUP_STREAM() etc.). Thus,



it takes two arguments, the character to display itself, and a reference to the underlying stream object, and it is expectedto return 0 upon success.

This function remembers the last unprocessed newline character seen in the function-local static variable nl_seen. Ifa newline character is encountered, it will simply set this variable to a true value, and return to the caller. As soon as thefirst non-newline character is to be displayed with nl_seen still true, the LCD controller is told to clear the display, putthe cursor home, and restart at SRAM address 0. All other characters are sent to the display.

The single static function-internal variable nl_seen works for this purpose. If multiple LCDs should be controlledusing the same set of driver functions, that would not work anymore, as a way is needed to distinguish between thevarious displays. This is where the second parameter can be used, the reference to the stream itself: instead of keepingthe state inside a private variable of the function, it can be kept inside a private object that is attached to the streamitself. A reference to that private object can be attached to the stream (e.g. inside the function lcd_init() thatthen also needs to be passed a reference to the stream) using fdev_set_udata(), and can be accessed insidelcd_putchar() using fdev_get_udata().

23.41.3.7 uart.h

Public interface definition for the RS-232 UART driver, much like in lcd.h except there is now also a character inputfunction available.

As the RS-232 input is line-buffered in this example, the macro RX_BUFSIZE determines the size of that buffer.

23.41.3.8 uart.c

This implements an stdio-compatible RS-232 driver using an AVR’s standard UART (or USART in asynchronous opera-tion mode). Both, character output as well as character input operations are implemented. Character output takes careof converting the internal newline \n into its external representation carriage return/line feed (\r\n).

Character input is organized as a line-buffered operation that allows to minimally edit the current line until it is "sent"to the application when either a carriage return (\r) or newline (\n) character is received from the terminal. The lineediting functions implemented are:

• \b (back space) or \177 (delete) deletes the previous character

• ∧u (control-U, ASCII NAK) deletes the entire input buffer

• ∧w (control-W, ASCII ETB) deletes the previous input word, delimited by white space

• ∧r (control-R, ASCII DC2) sends a \r, then reprints the buffer (refresh)

• \t (tabulator) will be replaced by a single space

The function uart_init() takes care of all hardware initialization that is required to put the UART into a mode with8 data bits, no parity, one stop bit (commonly referred to as 8N1) at the baud rate configured in defines.h. At low CPUclock frequencies, the U2X bit in the UART is set, reducing the oversampling from 16x to 8x, which allows for a 9600 Bdrate to be achieved with tolerable error using the default 1 MHz RC oscillator.

The public function uart_putchar() again has suitable arguments for direct use by the stdio stream interface. Itperforms the \n into \r\n translation by recursively calling itself when it sees a \n character. Just for demonstrationpurposes, the \a (audible bell, ASCII BEL) character is implemented by sending a string to stderr, so it will bedisplayed on the LCD.

The public function uart_getchar() implements the line editor. If there are characters available in the line buffer(variable rxp is not NULL), the next character will be returned from the buffer without any UART interaction.

If there are no characters inside the line buffer, the input loop will be entered. Characters will be read from the UART,and processed accordingly. If the UART signalled a framing error (FE bit set), typically caused by the terminal sendinga line break condition (start condition held much longer than one character period), the function will return an end-of-file


312 CONTENTS

condition using _FDEV_EOF. If there was a data overrun condition on input (DOR bit set), an error condition will bereturned as _FDEV_ERR.

Line editing characters are handled inside the loop, potentially modifying the buffer status. If characters are attemptedto be entered beyond the size of the line buffer, their reception is refused, and a \a character is sent to the terminal. Ifa \r or \n character is seen, the variable rxp (receive pointer) is set to the beginning of the buffer, the loop is left, andthe first character of the buffer will be returned to the application. (If no other characters have been entered, this will justbe the newline character, and the buffer is marked as being exhausted immediately again.)



$prefix/share/doc/avr-libc/examples/stdiodemo/,



23.42 Example using the two-wire interface (TWI) 313

23.42 Example using the two-wire interface (TWI)

Some newer devices of the ATmega series contain builtin support for interfacing the microcontroller to a two-wire bus,called TWI. This is essentially the same called I2C by Philips, but that term is avoided in Atmel’s documentation due topatenting issues.

For further documentation, see:

http://www.nxp.com/documents/user_manual/UM10204.pdf

23.42.1 Introduction into TWI

The two-wire interface consists of two signal lines named SDA (serial data) and SCL (serial clock) (plus a ground line, ofcourse). All devices participating in the bus are connected together, using open-drain driver circuitry, so the wires mustbe terminated using appropriate pullup resistors. The pullups must be small enough to recharge the line capacity in shortenough time compared to the desired maximal clock frequency, yet large enough so all drivers will not be overloaded.There are formulas in the datasheet that help selecting the pullups.

Devices can either act as a master to the bus (i. e., they initiate a transfer), or as a slave (they only act when beingcalled by a master). The bus is multi-master capable, and a particular device implementation can act as either masteror slave at different times. Devices are addressed using a 7-bit address (coordinated by Philips) transfered as the firstbyte after the so-called start condition. The LSB of that byte is R/∼W, i. e. it determines whether the request to theslave is to read or write data during the next cycles. (There is also an option to have devices using 10-bit addresses butthat is not covered by this example.)

23.42.2 The TWI example project

The ATmega TWI hardware supports both, master and slave operation. This example will only demonstrate how to usean AVR microcontroller as TWI master. The implementation is kept simple in order to concentrate on the steps that arerequired to talk to a TWI slave, so all processing is done in polled-mode, waiting for the TWI interface to indicate that thenext processing step is due (by setting the TWINT interrupt bit). If it is desired to have the entire TWI communicationhappen in "background", all this can be implemented in an interrupt-controlled way, where only the start condition needsto be triggered from outside the interrupt routine.

There is a variety of slave devices available that can be connected to a TWI bus. For the purpose of this example, anEEPROM device out of the industry-standard 24Cxx series has been chosen (where xx can be one of 01, 02, 04, 08, or16) which are available from various vendors. The choice was almost arbitrary, mainly triggered by the fact that an EE←↩PROM device is being talked to in both directions, reading and writing the slave device, so the example will demonstratethe details of both.

Usually, there is probably not much need to add more EEPROM to an ATmega system that way: the smallest possibleAVR device that offers hardware TWI support is the ATmega8 which comes with 512 bytes of EEPROM, which isequivalent to an 24C04 device. The ATmega128 already comes with twice as much EEPROM as the 24C16 wouldoffer. One exception might be to use an externally connected EEPROM device that is removable; e. g. SDRAM PCmemory comes with an integrated TWI EEPROM that carries the RAM configuration information.

23.42.3 The Source Code


$prefix/share/doc/avr-libc/examples/twitest/twitest.c,



http://www.nxp.com/documents/user_manual/UM10204.pdf

314 CONTENTS

Note [1]

The header file <util/twi.h> contains some macro definitions for symbolic constants used in the TWI statusregister. These definitions match the names used in the Atmel datasheet except that all names have been prefixed withTW_.

Note [2]

The clock is used in timer calculations done by the compiler, for the UART baud rate and the TWI clock rate.

Note [3]

The address assigned for the 24Cxx EEPROM consists of 1010 in the upper four bits. The following three bits arenormally available as slave sub-addresses, allowing to operate more than one device of the same type on a single bus,where the actual subaddress used for each device is configured by hardware strapping. However, since the next datapacket following the device selection only allows for 8 bits that are used as an EEPROM address, devices that requiremore than 8 address bits (24C04 and above) "steal" subaddress bits and use them for the EEPROM cell address bits 9to 11 as required. This example simply assumes all subaddress bits are 0 for the smaller devices, so the E0, E1, andE2 inputs of the 24Cxx must be grounded.

Note [3a]

EEPROMs of type 24C32 and above cannot be addressed anymore even with the subaddress bit trick. Thus, theyrequire the upper address bits being sent separately on the bus. When activating the WORD_ADDRESS_16BIT define,the algorithm implements that auxiliary address byte transmission.

Note [4]

For slow clocks, enable the 2 x U[S]ART clock multiplier, to improve the baud rate error. This will allow a 9600 Bdcommunication using the standard 1 MHz calibrated RC oscillator. See also the Baud rate tables in the datasheets.

Note [5]

The datasheet explains why a minimum TWBR value of 10 should be maintained when running in master mode. Thus,for system clocks below 3.6 MHz, we cannot run the bus at the intented clock rate of 100 kHz but have to slow downaccordingly.

Note [6]

This function is used by the standard output facilities that are utilized in this example for debugging and demonstrationpurposes.


23.42 Example using the two-wire interface (TWI) 315

Note [7]

In order to shorten the data to be sent over the TWI bus, the 24Cxx EEPROMs support multiple data bytes transferedwithin a single request, maintaining an internal address counter that is updated after each data byte transfered success-fully. When reading data, one request can read the entire device memory if desired (the counter would wrap around andstart back from 0 when reaching the end of the device).

Note [8]

When reading the EEPROM, a first device selection must be made with write intent (R/∼W bit set to 0 indicating a writeoperation) in order to transfer the EEPROM address to start reading from. This is called master transmitter mode. Eachcompletion of a particular step in TWI communication is indicated by an asserted TWINT bit in TWCR. (An interruptwould be generated if allowed.) After performing any actions that are needed for the next communication step, theinterrupt condition must be manually cleared by setting the TWINT bit. Unlike with many other interrupt sources, thiswould even be required when using a true interrupt routine, since as soon as TWINT is re-asserted, the next bustransaction will start.

Note [9]

Since the TWI bus is multi-master capable, there is potential for a bus contention when one master starts to accessthe bus. Normally, the TWI bus interface unit will detect this situation, and will not initiate a start condition while thebus is busy. However, in case two masters were starting at exactly the same time, the way bus arbitration works, thereis always a chance that one master could lose arbitration of the bus during any transmit operation. A master that haslost arbitration is required by the protocol to immediately cease talking on the bus; in particular it must not initiate astop condition in order to not corrupt the ongoing transfer from the active master. In this example, upon detecting a lostarbitration condition, the entire transfer is going to be restarted. This will cause a new start condition to be initiated,which will normally be delayed until the currently active master has released the bus.

Note [10]

Next, the device slave is going to be reselected (using a so-called repeated start condition which is meant to guaranteethat the bus arbitration will remain at the current master) using the same slave address (SLA), but this time with readintent (R/∼W bit set to 1) in order to request the device slave to start transfering data from the slave to the master in thenext packet.

Note [11]

If the EEPROM device is still busy writing one or more cells after a previous write request, it will simply leave its businterface drivers at high impedance, and does not respond to a selection in any way at all. The master selecting thedevice will see the high level at SDA after transfering the SLA+R/W packet as a NACK to its selection request. Thus,the select process is simply started over (effectively causing a repeated start condition), until the device will eventuallyrespond. This polling procedure is recommended in the 24Cxx datasheet in order to minimize the busy wait time whenwriting. Note that in case a device is broken and never responds to a selection (e. g. since it is no longer present atall), this will cause an infinite loop. Thus the maximal number of iterations made until the device is declared to be notresponding at all, and an error is returned, will be limited to MAX_ITER.


316 CONTENTS

Note [12]

This is called master receiver mode: the bus master still supplies the SCL clock, but the device slave drives the SDA linewith the appropriate data. After 8 data bits, the master responds with an ACK bit (SDA driven low) in order to requestanother data transfer from the slave, or it can leave the SDA line high (NACK), indicating to the slave that it is going tostop the transfer now. Assertion of ACK is handled by setting the TWEA bit in TWCR when starting the current transfer.

Note [13]

The control word sent out in order to initiate the transfer of the next data packet is initially set up to assert the TWEA bit.During the last loop iteration, TWEA is de-asserted so the client will get informed that no further transfer is desired.

Note [14]

Except in the case of lost arbitration, all bus transactions must properly be terminated by the master initiating a stopcondition.

Note [15]

Writing to the EEPROM device is simpler than reading, since only a master transmitter mode transfer is needed. Notethat the first packet after the SLA+W selection is always considered to be the EEPROM address for the next operation.(This packet is exactly the same as the one above sent before starting to read the device.) In case a master transmittermode transfer is going to send more than one data packet, all following packets will be considered data bytes to write atthe indicated address. The internal address pointer will be incremented after each write operation.

Note [16]

24Cxx devices can become write-protected by strapping their∼WC pin to logic high. (Leaving it unconnected is explicitlyallowed, and constitutes logic low level, i. e. no write protection.) In case of a write protected device, all data transferattempts will be NACKed by the device. Note that some devices might not implement this.


24 Data Structure Documentation 317

24 Data Structure Documentation

24.1 atexit_s Struct Reference

Data Fields

• void(∗ fun )(void)• struct atexit_s ∗ next

The documentation for this struct was generated from the following file:

• atexit.c

24.2 div_t Struct Reference

Data Fields

• int quot• int rem


Result type for function div().

24.2.2 Field Documentation

24.2.2.1 int div_t::quot

The Quotient.

24.2.2.2 int div_t::rem

The Remainder.


• stdlib.h

24.3 ldiv_t Struct Reference

Data Fields

• long quot• long rem


Result type for function ldiv().


318 CONTENTS

24.3.2 Field Documentation

24.3.2.1 long ldiv_t::quot

The Quotient.

24.3.2.2 long ldiv_t::rem

The Remainder.


• stdlib.h

24.4 tm Struct Reference

Data Fields

• int8_t tm_sec• int8_t tm_min• int8_t tm_hour• int8_t tm_mday• int8_t tm_wday• int8_t tm_mon• int16_t tm_year• int16_t tm_yday• int16_t tm_isdst


The tm structure contains a representation of time ’broken down’ into components of the Gregorian calendar.

The normal ranges of the elements are..

tm_sec seconds after the minute - [ 0 to 59 ]tm_min minutes after the hour - [ 0 to 59 ]tm_hour hours since midnight - [ 0 to 23 ]tm_mday day of the month - [ 1 to 31 ]tm_wday days since Sunday - [ 0 to 6 ]tm_mon months since January - [ 0 to 11 ]tm_year years since 1900tm_yday days since January 1 - [ 0 to 365 ]tm_isdst Daylight Saving Time flag *

The value of tm_isdst is zero if Daylight Saving Time is not in effect, and is negative ifthe information is not available.

When Daylight Saving Time is in effect, the value represents the number ofseconds the clock is advanced.

See the set_dst() function for more information about Daylight Saving.


• time.h


24.5 week_date Struct Reference 319

24.5 week_date Struct Reference

Data Fields

• int year• int week• int day


Structure which represents a date as a year, week number of that year, and day of week. See http://en.←↩wikipedia.org/wiki/ISO_week_date for more information.


• time.h

25 File Documentation

25.1 assert.h File Reference

Macros

• #define assert(expression)

25.2 atoi.S File Reference

25.3 atol.S File Reference

25.4 atomic.h File Reference

Macros

• #define ATOMIC_BLOCK(type)• #define NONATOMIC_BLOCK(type)• #define ATOMIC_RESTORESTATE• #define ATOMIC_FORCEON• #define NONATOMIC_RESTORESTATE• #define NONATOMIC_FORCEOFF

25.5 boot.h File Reference

Macros

• #define BOOTLOADER_SECTION __attribute__ ((section (".bootloader")))• #define __COMMON_ASB RWWSB• #define __COMMON_ASRE RWWSRE• #define BLB12 5• #define BLB11 4




320 CONTENTS

• #define BLB02 3

• #define BLB01 2

• #define boot_spm_interrupt_enable() (__SPM_REG |= (uint8_t)_BV(SPMIE))

• #define boot_spm_interrupt_disable() (__SPM_REG &= (uint8_t)∼_BV(SPMIE))

• #define boot_is_spm_interrupt() (__SPM_REG & (uint8_t)_BV(SPMIE))

• #define boot_rww_busy() (__SPM_REG & (uint8_t)_BV(__COMMON_ASB))

• #define boot_spm_busy() (__SPM_REG & (uint8_t)_BV(__SPM_ENABLE))

• #define boot_spm_busy_wait() do{}while(boot_spm_busy())

• #define __BOOT_PAGE_ERASE (_BV(__SPM_ENABLE) | _BV(PGERS))

• #define __BOOT_PAGE_WRITE (_BV(__SPM_ENABLE) | _BV(PGWRT))

• #define __BOOT_PAGE_FILL _BV(__SPM_ENABLE)

• #define __BOOT_RWW_ENABLE (_BV(__SPM_ENABLE) | _BV(__COMMON_ASRE))

• #define __boot_page_fill_normal(address, data)

• #define __boot_page_fill_alternate(address, data)

• #define __boot_page_fill_extended(address, data)

• #define __boot_page_erase_normal(address)

• #define __boot_page_erase_alternate(address)

• #define __boot_page_erase_extended(address)

• #define __boot_page_write_normal(address)

• #define __boot_page_write_alternate(address)

• #define __boot_page_write_extended(address)

• #define __boot_rww_enable()

• #define __boot_rww_enable_alternate()

• #define __boot_lock_bits_set(lock_bits)

• #define __boot_lock_bits_set_alternate(lock_bits)

• #define GET_LOW_FUSE_BITS (0x0000)

• #define GET_LOCK_BITS (0x0001)

• #define GET_EXTENDED_FUSE_BITS (0x0002)

• #define GET_HIGH_FUSE_BITS (0x0003)

• #define boot_lock_fuse_bits_get(address)

• #define __BOOT_SIGROW_READ (_BV(__SPM_ENABLE) | _BV(SIGRD))

• #define boot_signature_byte_get(addr)

• #define boot_page_fill(address, data) __boot_page_fill_normal(address, data)

• #define boot_page_erase(address) __boot_page_erase_normal(address)

• #define boot_page_write(address) __boot_page_write_normal(address)

• #define boot_rww_enable() __boot_rww_enable()

• #define boot_lock_bits_set(lock_bits) __boot_lock_bits_set(lock_bits)

• #define boot_page_fill_safe(address, data)

• #define boot_page_erase_safe(address)

• #define boot_page_write_safe(address)

• #define boot_rww_enable_safe()

• #define boot_lock_bits_set_safe(lock_bits)


25.5 boot.h File Reference 321


25.5.1.1 #define __boot_lock_bits_set( lock_bits )

Value:

(__extension__({ \uint8_t value = (uint8_t)(~(lock_bits)); \__asm__ __volatile__ $ \

"ldi r30, 1\n\t" \"ldi r31, 0\n\t" \"mov r0, %2\n\t" \"sts %0, %1\n\t" \"spm\n\t" \: \: "i" (_SFR_MEM_ADDR(__SPM_REG)), \"r" ((uint8_t)(__BOOT_LOCK_BITS_SET)), \"r" (value) \

: "r0", "r30", "r31" $; \

}))

25.5.1.2 #define __boot_lock_bits_set_alternate( lock_bits )

Value:

(__extension__({ \uint8_t value = (uint8_t)(~(lock_bits)); \__asm__ __volatile__ $ \

"ldi r30, 1\n\t" \"ldi r31, 0\n\t" \"mov r0, %2\n\t" \"sts %0, %1\n\t" \"spm\n\t" \".word 0xffff\n\t" \"nop\n\t" \: \: "i" (_SFR_MEM_ADDR(__SPM_REG)), \"r" ((uint8_t)(__BOOT_LOCK_BITS_SET)), \"r" (value) \

: "r0", "r30", "r31" $; \

}))

25.5.1.3 #define __boot_page_erase_alternate( address )

Value:

(__extension__({ \__asm__ __volatile__ \( \

"sts %0, %1\n\t" \"spm\n\t" \".word 0xffff\n\t" \"nop\n\t" \: \: "i" (_SFR_MEM_ADDR(__SPM_REG)), \"r" ((uint8_t)(__BOOT_PAGE_ERASE)), \"z" ((uint16_t)(address)) \

); \}))

25.5.1.4 #define __boot_page_erase_extended( address )

Value:


322 CONTENTS


"movw r30, %A3\n\t" \"sts %1, %C3\n\t" \"sts %0, %2\n\t" \"spm\n\t" \: \: "i" (_SFR_MEM_ADDR(__SPM_REG)), \"i" (_SFR_MEM_ADDR(RAMPZ)), \"r" ((uint8_t)(__BOOT_PAGE_ERASE)), \"r" ((uint32_t)(address)) \

: "r30", "r31" \); \

}))

25.5.1.5 #define __boot_page_erase_normal( address )

Value:


"sts %0, %1\n\t" \"spm\n\t" \: \: "i" (_SFR_MEM_ADDR(__SPM_REG)), \"r" ((uint8_t)(__BOOT_PAGE_ERASE)), \"z" ((uint16_t)(address)) \

); \}))

25.5.1.6 #define __boot_page_fill_alternate( address, data )

Value:


"movw r0, %3\n\t" \"sts %0, %1\n\t" \"spm\n\t" \".word 0xffff\n\t" \"nop\n\t" \"clr r1\n\t" \: \: "i" (_SFR_MEM_ADDR(__SPM_REG)), \"r" ((uint8_t)(__BOOT_PAGE_FILL)), \"z" ((uint16_t)(address)), \"r" ((uint16_t)(data)) \

: "r0" \); \

}))

25.5.1.7 #define __boot_page_fill_extended( address, data )

Value:


"movw r0, %4\n\t" \"movw r30, %A3\n\t" \"sts %1, %C3\n\t" \"sts %0, %2\n\t" \"spm\n\t" \"clr r1\n\t" \: \: "i" (_SFR_MEM_ADDR(__SPM_REG)), \"i" (_SFR_MEM_ADDR(RAMPZ)), \


25.5 boot.h File Reference 323

"r" ((uint8_t)(__BOOT_PAGE_FILL)), \"r" ((uint32_t)(address)), \"r" ((uint16_t)(data)) \

: "r0", "r30", "r31" \); \

}))

25.5.1.8 #define __boot_page_fill_normal( address, data )

Value:


"movw r0, %3\n\t" \"sts %0, %1\n\t" \"spm\n\t" \"clr r1\n\t" \: \: "i" (_SFR_MEM_ADDR(__SPM_REG)), \

"r" ((uint8_t)(__BOOT_PAGE_FILL)), \"z" ((uint16_t)(address)), \"r" ((uint16_t)(data)) \

: "r0" \); \

}))

25.5.1.9 #define __boot_page_write_alternate( address )

Value:


"sts %0, %1\n\t" \"spm\n\t" \".word 0xffff\n\t" \"nop\n\t" \: \: "i" (_SFR_MEM_ADDR(__SPM_REG)), \"r" ((uint8_t)(__BOOT_PAGE_WRITE)), \"z" ((uint16_t)(address)) \

); \}))

25.5.1.10 #define __boot_page_write_extended( address )

Value:


"movw r30, %A3\n\t" \"sts %1, %C3\n\t" \"sts %0, %2\n\t" \"spm\n\t" \: \: "i" (_SFR_MEM_ADDR(__SPM_REG)), \

"i" (_SFR_MEM_ADDR(RAMPZ)), \"r" ((uint8_t)(__BOOT_PAGE_WRITE)), \"r" ((uint32_t)(address)) \

: "r30", "r31" \); \

}))

25.5.1.11 #define __boot_page_write_normal( address )

Value:


324 CONTENTS


"sts %0, %1\n\t" \"spm\n\t" \: \: "i" (_SFR_MEM_ADDR(__SPM_REG)), \"r" ((uint8_t)(__BOOT_PAGE_WRITE)), \"z" ((uint16_t)(address)) \

); \}))

25.5.1.12 #define __boot_rww_enable( )

Value:


"sts %0, %1\n\t" \"spm\n\t" \: \: "i" (_SFR_MEM_ADDR(__SPM_REG)), \"r" ((uint8_t)(__BOOT_RWW_ENABLE)) \

); \}))

25.5.1.13 #define __boot_rww_enable_alternate( )

Value:


"sts %0, %1\n\t" \"spm\n\t" \".word 0xffff\n\t" \"nop\n\t" \: \: "i" (_SFR_MEM_ADDR(__SPM_REG)), \"r" ((uint8_t)(__BOOT_RWW_ENABLE)) \

); \}))

25.6 cpufunc.h File Reference

Macros

• #define _NOP()• #define _MemoryBarrier()

25.7 crc16.h File Reference

Functions

• static __inline__ uint16_t _crc16_update (uint16_t __crc, uint8_t __data)• static __inline__ uint16_t _crc_xmodem_update (uint16_t __crc, uint8_t __data)• static __inline__ uint16_t _crc_ccitt_update (uint16_t __crc, uint8_t __data)• static __inline__ uint8_t _crc_ibutton_update (uint8_t __crc, uint8_t __data)• static __inline__ uint8_t _crc8_ccitt_update (uint8_t __crc, uint8_t __data)


25.8 ctype.h File Reference 325

25.8 ctype.h File Reference

Functions

Character classification routines

These functions perform character classification. They return true or false status depending whether the characterpassed to the function falls into the function’s classification (i.e. isdigit() returns true if its argument is any value ’0’though ’9’, inclusive). If the input is not an unsigned char value, all of this function return false.

• int isalnum (int __c)• int isalpha (int __c)• int isascii (int __c)• int isblank (int __c)• int iscntrl (int __c)• int isdigit (int __c)• int isgraph (int __c)• int islower (int __c)• int isprint (int __c)• int ispunct (int __c)• int isspace (int __c)• int isupper (int __c)• int isxdigit (int __c)

Character convertion routines

This realization permits all possible values of integer argument. The toascii() function clears all highest bits. Thetolower() and toupper() functions return an input argument as is, if it is not an unsigned char value.

• int toascii (int __c)• int tolower (int __c)• int toupper (int __c)

25.9 delay.h File Reference

Macros

• #define __HAS_DELAY_CYCLES 1

• #define F_CPU 1000000UL

Functions

• void _delay_ms (double __ms)

• void _delay_us (double __us)

25.10 delay_basic.h File Reference

Functions

• void _delay_loop_1 (uint8_t __count)

• void _delay_loop_2 (uint16_t __count)


326 CONTENTS

25.11 errno.h File Reference

Macros

• #define EDOM 33• #define ERANGE 34• #define ENOSYS ((int)(66081697 & 0x7fff))• #define EINTR ((int)(2453066 & 0x7fff))• #define E2BIG ENOERR• #define EACCES ENOERR• #define EADDRINUSE ENOERR• #define EADDRNOTAVAIL ENOERR• #define EAFNOSUPPORT ENOERR• #define EAGAIN ENOERR• #define EALREADY ENOERR• #define EBADF ENOERR• #define EBUSY ENOERR• #define ECHILD ENOERR• #define ECONNABORTED ENOERR• #define ECONNREFUSED ENOERR• #define ECONNRESET ENOERR• #define EDEADLK ENOERR• #define EDESTADDRREQ ENOERR• #define EEXIST ENOERR• #define EFAULT ENOERR• #define EFBIG ENOERR• #define EHOSTUNREACH ENOERR• #define EILSEQ ENOERR• #define EINPROGRESS ENOERR• #define EINVAL ENOERR• #define EIO ENOERR• #define EISCONN ENOERR• #define EISDIR ENOERR• #define ELOOP ENOERR• #define EMFILE ENOERR• #define EMLINK ENOERR• #define EMSGSIZE ENOERR• #define ENAMETOOLONG ENOERR• #define ENETDOWN ENOERR• #define ENETRESET ENOERR• #define ENETUNREACH ENOERR• #define ENFILE ENOERR• #define ENOBUFS ENOERR• #define ENODEV ENOERR• #define ENOENT ENOERR• #define ENOEXEC ENOERR• #define ENOLCK ENOERR• #define ENOMEM ENOERR• #define ENOMSG ENOERR• #define ENOPROTOOPT ENOERR• #define ENOSPC ENOERR


25.12 fdevopen.c File Reference 327

• #define ENOTCONN ENOERR• #define ENOTDIR ENOERR• #define ENOTEMPTY ENOERR• #define ENOTSOCK ENOERR• #define ENOTTY ENOERR• #define ENXIO ENOERR• #define EOPNOTSUPP ENOERR• #define EPERM ENOERR• #define EPIPE ENOERR• #define EPROTONOSUPPORT ENOERR• #define EPROTOTYPE ENOERR• #define EROFS ENOERR• #define ESPIPE ENOERR• #define ESRCH ENOERR• #define ETIMEDOUT ENOERR• #define EWOULDBLOCK ENOERR• #define EXDEV ENOERR• #define ENOERR ((int)(66072050 & 0xffff))

Variables

• int errno

25.12 fdevopen.c File Reference

Functions

• FILE ∗ fdevopen (int(∗put)(char, FILE ∗), int(∗get)(FILE ∗))

25.13 ffs.S File Reference

25.14 ffsl.S File Reference

25.15 ffsll.S File Reference

25.16 fuse.h File Reference

Macros

• #define FUSEMEM __attribute__((__used__, __section__ (".fuse")))• #define FUSES __fuse_t __fuse FUSEMEM

25.17 interrupt.h File Reference

Macros

Global manipulation of the interrupt flag

The global interrupt flag is maintained in the I bit of the status register (SREG).


328 CONTENTS

Handling interrupts frequently requires attention regarding atomic access to objects that could be altered by coderunning within an interrupt context, see <util/atomic.h>.

Frequently, interrupts are being disabled for periods of time in order to perform certain operations without being dis-turbed; see Problems with reordering code for things to be taken into account with respect to compiler optimizations.

• #define sei()• #define cli()

Macros for writing interrupt handler functions

• #define ISR(vector, attributes)• #define SIGNAL(vector)• #define EMPTY_INTERRUPT(vector)• #define ISR_ALIAS(vector, target_vector)• #define reti()• #define BADISR_vect

ISR attributes

• #define ISR_BLOCK• #define ISR_NOBLOCK• #define ISR_NAKED• #define ISR_ALIASOF(target_vector)


@{

25.18 inttypes.h File Reference

Macros

macros for printf and scanf format specifiers

For C++, these are only included if __STDC_LIMIT_MACROS is defined before including <inttypes.h>.

• #define PRId8 "d"• #define PRIdLEAST8 "d"• #define PRIdFAST8 "d"• #define PRIi8 "i"• #define PRIiLEAST8 "i"• #define PRIiFAST8 "i"• #define PRId16 "d"• #define PRIdLEAST16 "d"• #define PRIdFAST16 "d"• #define PRIi16 "i"• #define PRIiLEAST16 "i"• #define PRIiFAST16 "i"• #define PRId32 "ld"• #define PRIdLEAST32 "ld"• #define PRIdFAST32 "ld"• #define PRIi32 "li"• #define PRIiLEAST32 "li"• #define PRIiFAST32 "li"• #define PRIdPTR PRId16• #define PRIiPTR PRIi16


25.18 inttypes.h File Reference 329

• #define PRIo8 "o"• #define PRIoLEAST8 "o"• #define PRIoFAST8 "o"• #define PRIu8 "u"• #define PRIuLEAST8 "u"• #define PRIuFAST8 "u"• #define PRIx8 "x"• #define PRIxLEAST8 "x"• #define PRIxFAST8 "x"• #define PRIX8 "X"• #define PRIXLEAST8 "X"• #define PRIXFAST8 "X"• #define PRIo16 "o"• #define PRIoLEAST16 "o"• #define PRIoFAST16 "o"• #define PRIu16 "u"• #define PRIuLEAST16 "u"• #define PRIuFAST16 "u"• #define PRIx16 "x"• #define PRIxLEAST16 "x"• #define PRIxFAST16 "x"• #define PRIX16 "X"• #define PRIXLEAST16 "X"• #define PRIXFAST16 "X"• #define PRIo32 "lo"• #define PRIoLEAST32 "lo"• #define PRIoFAST32 "lo"• #define PRIu32 "lu"• #define PRIuLEAST32 "lu"• #define PRIuFAST32 "lu"• #define PRIx32 "lx"• #define PRIxLEAST32 "lx"• #define PRIxFAST32 "lx"• #define PRIX32 "lX"• #define PRIXLEAST32 "lX"• #define PRIXFAST32 "lX"• #define PRIoPTR PRIo16• #define PRIuPTR PRIu16• #define PRIxPTR PRIx16• #define PRIXPTR PRIX16• #define SCNd8 "hhd"• #define SCNdLEAST8 "hhd"• #define SCNdFAST8 "hhd"• #define SCNi8 "hhi"• #define SCNiLEAST8 "hhi"• #define SCNiFAST8 "hhi"• #define SCNd16 "d"• #define SCNdLEAST16 "d"• #define SCNdFAST16 "d"• #define SCNi16 "i"• #define SCNiLEAST16 "i"• #define SCNiFAST16 "i"• #define SCNd32 "ld"• #define SCNdLEAST32 "ld"• #define SCNdFAST32 "ld"• #define SCNi32 "li"• #define SCNiLEAST32 "li"• #define SCNiFAST32 "li"• #define SCNdPTR SCNd16• #define SCNiPTR SCNi16


330 CONTENTS

• #define SCNo8 "hho"• #define SCNoLEAST8 "hho"• #define SCNoFAST8 "hho"• #define SCNu8 "hhu"• #define SCNuLEAST8 "hhu"• #define SCNuFAST8 "hhu"• #define SCNx8 "hhx"• #define SCNxLEAST8 "hhx"• #define SCNxFAST8 "hhx"• #define SCNo16 "o"• #define SCNoLEAST16 "o"• #define SCNoFAST16 "o"• #define SCNu16 "u"• #define SCNuLEAST16 "u"• #define SCNuFAST16 "u"• #define SCNx16 "x"• #define SCNxLEAST16 "x"• #define SCNxFAST16 "x"• #define SCNo32 "lo"• #define SCNoLEAST32 "lo"• #define SCNoFAST32 "lo"• #define SCNu32 "lu"• #define SCNuLEAST32 "lu"• #define SCNuFAST32 "lu"• #define SCNx32 "lx"• #define SCNxLEAST32 "lx"• #define SCNxFAST32 "lx"• #define SCNoPTR SCNo16• #define SCNuPTR SCNu16• #define SCNxPTR SCNx16

Typedefs

Far pointers for memory access >64K

• typedef int32_t int_farptr_t• typedef uint32_t uint_farptr_t

25.19 io.h File Reference

25.20 lock.h File Reference

Macros

• #define LOCKMEM __attribute__((__used__, __section__ (".lock")))• #define LOCKBITS unsigned char __lock LOCKMEM• #define LOCKBITS_DEFAULT (0xFF)

25.21 math.h File Reference

Macros

• #define M_E 2.7182818284590452354• #define M_LOG2E 1.4426950408889634074 /∗ log_2 e ∗/


25.21 math.h File Reference 331

• #define M_LOG10E 0.43429448190325182765 /∗ log_10 e ∗/• #define M_LN2 0.69314718055994530942 /∗ log_e 2 ∗/• #define M_LN10 2.30258509299404568402 /∗ log_e 10 ∗/• #define M_PI 3.14159265358979323846 /∗ pi ∗/• #define M_PI_2 1.57079632679489661923 /∗ pi/2 ∗/• #define M_PI_4 0.78539816339744830962 /∗ pi/4 ∗/• #define M_1_PI 0.31830988618379067154 /∗ 1/pi ∗/• #define M_2_PI 0.63661977236758134308 /∗ 2/pi ∗/• #define M_2_SQRTPI 1.12837916709551257390 /∗ 2/sqrt(pi) ∗/• #define M_SQRT2 1.41421356237309504880 /∗ sqrt(2) ∗/• #define M_SQRT1_2 0.70710678118654752440 /∗ 1/sqrt(2) ∗/• #define NAN __builtin_nan("")• #define INFINITY __builtin_inf()• #define cosf cos• #define sinf sin• #define tanf tan• #define fabsf fabs• #define fmodf fmod• #define cbrtf cbrt• #define hypotf hypot• #define squaref square• #define floorf floor• #define ceilf ceil• #define frexpf frexp• #define ldexpf ldexp• #define expf exp• #define coshf cosh• #define sinhf sinh• #define tanhf tanh• #define acosf acos• #define asinf asin• #define atanf atan• #define atan2f atan2• #define logf log• #define log10f log10• #define powf pow• #define isnanf isnan• #define isinff isinf• #define isfinitef isfinite• #define copysignf copysign• #define signbitf signbit• #define fdimf fdim• #define fmaf fma• #define fmaxf fmax• #define fminf fmin• #define truncf trunc• #define roundf round• #define lroundf lround• #define lrintf lrint


332 CONTENTS

Functions

• double cos (double __x)

• double sin (double __x)

• double tan (double __x)

• double fabs (double __x)

• double fmod (double __x, double __y)

• double modf (double __x, double ∗__iptr)

• float modff (float __x, float ∗__iptr)

• double sqrt (double __x)

• float sqrtf (float)

• double cbrt (double __x)

• double hypot (double __x, double __y)

• double square (double __x)

• double floor (double __x)

• double ceil (double __x)

• double frexp (double __x, int ∗__pexp)

• double ldexp (double __x, int __exp)

• double exp (double __x)

• double cosh (double __x)

• double sinh (double __x)

• double tanh (double __x)

• double acos (double __x)

• double asin (double __x)

• double atan (double __x)

• double atan2 (double __y, double __x)

• double log (double __x)

• double log10 (double __x)

• double pow (double __x, double __y)

• int isnan (double __x)

• int isinf (double __x)

• static int isfinite (double __x)

• static double copysign (double __x, double __y)

• int signbit (double __x)

• double fdim (double __x, double __y)

• double fma (double __x, double __y, double __z)

• double fmax (double __x, double __y)

• double fmin (double __x, double __y)

• double trunc (double __x)

• double round (double __x)

• long lround (double __x)

• long lrint (double __x)


25.22 memccpy.S File Reference 333

25.22 memccpy.S File Reference

25.23 memchr.S File Reference

25.24 memchr_P.S File Reference

25.25 memcmp.S File Reference

25.26 memcmp_P.S File Reference

25.27 memcmp_PF.S File Reference

25.28 memcpy.S File Reference

25.29 memcpy_P.S File Reference

25.30 memmem.S File Reference

25.31 memmove.S File Reference

25.32 memrchr.S File Reference

25.33 memrchr_P.S File Reference

25.34 memset.S File Reference

25.35 parity.h File Reference

Macros

• #define parity_even_bit(val)

25.36 pgmspace.h File Reference

Macros

• #define __need_size_t• #define __ATTR_PROGMEM__ __attribute__((__progmem__))• #define __ATTR_PURE__ __attribute__((__pure__))• #define PROGMEM __ATTR_PROGMEM__• #define PGM_P const char ∗• #define PGM_VOID_P const void ∗• #define PSTR(s) ((const PROGMEM char ∗)(s))• #define __LPM_classic__(addr)• #define __LPM_enhanced__(addr)• #define __LPM_word_classic__(addr)• #define __LPM_word_enhanced__(addr)• #define __LPM_dword_classic__(addr)• #define __LPM_dword_enhanced__(addr)


334 CONTENTS

• #define __LPM_float_classic__(addr)• #define __LPM_float_enhanced__(addr)• #define __LPM(addr) __LPM_classic__(addr)• #define __LPM_word(addr) __LPM_word_classic__(addr)• #define __LPM_dword(addr) __LPM_dword_classic__(addr)• #define __LPM_float(addr) __LPM_float_classic__(addr)• #define pgm_read_byte_near(address_short) __LPM((uint16_t)(address_short))• #define pgm_read_word_near(address_short) __LPM_word((uint16_t)(address_short))• #define pgm_read_dword_near(address_short) __LPM_dword((uint16_t)(address_short))• #define pgm_read_float_near(address_short) __LPM_float((uint16_t)(address_short))• #define pgm_read_ptr_near(address_short) (void∗)__LPM_word((uint16_t)(address_short))• #define __ELPM_classic__(addr)• #define __ELPM_enhanced__(addr)• #define __ELPM_xmega__(addr)• #define __ELPM_word_classic__(addr)• #define __ELPM_word_enhanced__(addr)• #define __ELPM_word_xmega__(addr)• #define __ELPM_dword_classic__(addr)• #define __ELPM_dword_enhanced__(addr)• #define __ELPM_dword_xmega__(addr)• #define __ELPM_float_classic__(addr)• #define __ELPM_float_enhanced__(addr)• #define __ELPM_float_xmega__(addr)• #define __ELPM(addr) __ELPM_classic__(addr)• #define __ELPM_word(addr) __ELPM_word_classic__(addr)• #define __ELPM_dword(addr) __ELPM_dword_classic__(addr)• #define __ELPM_float(addr) __ELPM_float_classic__(addr)• #define pgm_read_byte_far(address_long) __ELPM((uint32_t)(address_long))• #define pgm_read_word_far(address_long) __ELPM_word((uint32_t)(address_long))• #define pgm_read_dword_far(address_long) __ELPM_dword((uint32_t)(address_long))• #define pgm_read_float_far(address_long) __ELPM_float((uint32_t)(address_long))• #define pgm_read_ptr_far(address_long) (void∗)__ELPM_word((uint32_t)(address_long))• #define pgm_read_byte(address_short) pgm_read_byte_near(address_short)• #define pgm_read_word(address_short) pgm_read_word_near(address_short)• #define pgm_read_dword(address_short) pgm_read_dword_near(address_short)• #define pgm_read_float(address_short) pgm_read_float_near(address_short)• #define pgm_read_ptr(address_short) pgm_read_ptr_near(address_short)• #define pgm_get_far_address(var)

Typedefs

• typedef void PROGMEM prog_void• typedef char PROGMEM prog_char• typedef unsigned char PROGMEM prog_uchar• typedef int8_t PROGMEM prog_int8_t• typedef uint8_t PROGMEM prog_uint8_t• typedef int16_t PROGMEM prog_int16_t• typedef uint16_t PROGMEM prog_uint16_t• typedef int32_t PROGMEM prog_int32_t• typedef uint32_t PROGMEM prog_uint32_t• typedef int64_t PROGMEM prog_int64_t• typedef uint64_t PROGMEM prog_uint64_t


25.36 pgmspace.h File Reference 335

Functions

• const void ∗ memchr_P (const void ∗, int __val, size_t __len)• int memcmp_P (const void ∗, const void ∗, size_t) __ATTR_PURE__• void ∗ memccpy_P (void ∗, const void ∗, int __val, size_t)• void ∗ memcpy_P (void ∗, const void ∗, size_t)• void ∗ memmem_P (const void ∗, size_t, const void ∗, size_t) __ATTR_PURE__• const void ∗ memrchr_P (const void ∗, int __val, size_t __len)• char ∗ strcat_P (char ∗, const char ∗)• const char ∗ strchr_P (const char ∗, int __val)• const char ∗ strchrnul_P (const char ∗, int __val)• int strcmp_P (const char ∗, const char ∗) __ATTR_PURE__• char ∗ strcpy_P (char ∗, const char ∗)• int strcasecmp_P (const char ∗, const char ∗) __ATTR_PURE__• char ∗ strcasestr_P (const char ∗, const char ∗) __ATTR_PURE__• size_t strcspn_P (const char ∗__s, const char ∗__reject) __ATTR_PURE__• size_t strlcat_P (char ∗, const char ∗, size_t)• size_t strlcpy_P (char ∗, const char ∗, size_t)• size_t __strlen_P (const char ∗)• size_t strnlen_P (const char ∗, size_t)• int strncmp_P (const char ∗, const char ∗, size_t) __ATTR_PURE__• int strncasecmp_P (const char ∗, const char ∗, size_t) __ATTR_PURE__• char ∗ strncat_P (char ∗, const char ∗, size_t)• char ∗ strncpy_P (char ∗, const char ∗, size_t)• char ∗ strpbrk_P (const char ∗__s, const char ∗__accept) __ATTR_PURE__• const char ∗ strrchr_P (const char ∗, int __val)• char ∗ strsep_P (char ∗∗__sp, const char ∗__delim)• size_t strspn_P (const char ∗__s, const char ∗__accept) __ATTR_PURE__• char ∗ strstr_P (const char ∗, const char ∗) __ATTR_PURE__• char ∗ strtok_P (char ∗__s, const char ∗__delim)• char ∗ strtok_rP (char ∗__s, const char ∗__delim, char ∗∗__last)• size_t strlen_PF (uint_farptr_t src)• size_t strnlen_PF (uint_farptr_t src, size_t len)• void ∗ memcpy_PF (void ∗dest, uint_farptr_t src, size_t len)• char ∗ strcpy_PF (char ∗dest, uint_farptr_t src)• char ∗ strncpy_PF (char ∗dest, uint_farptr_t src, size_t len)• char ∗ strcat_PF (char ∗dest, uint_farptr_t src)• size_t strlcat_PF (char ∗dst, uint_farptr_t src, size_t siz)• char ∗ strncat_PF (char ∗dest, uint_farptr_t src, size_t len)• int strcmp_PF (const char ∗s1, uint_farptr_t s2) __ATTR_PURE__• int strncmp_PF (const char ∗s1, uint_farptr_t s2, size_t n) __ATTR_PURE__• int strcasecmp_PF (const char ∗s1, uint_farptr_t s2) __ATTR_PURE__• int strncasecmp_PF (const char ∗s1, uint_farptr_t s2, size_t n) __ATTR_PURE__• char ∗ strstr_PF (const char ∗s1, uint_farptr_t s2)• size_t strlcpy_PF (char ∗dst, uint_farptr_t src, size_t siz)• int memcmp_PF (const void ∗, uint_farptr_t, size_t) __ATTR_PURE__• __attribute__ ((__always_inline__)) static __inline__ size_t strlen_P(const char ∗s)• static __inline__ size_t strlen_P (const char ∗s)


336 CONTENTS


25.36.1.1 #define __ELPM_classic__( addr )

Value:

(__extension__({ \uint32_t __addr32 = (uint32_t)(addr); \uint8_t __result; \__asm__ __volatile__ $ \

"out %2, %C1" "\n\t" \"mov r31, %B1" "\n\t" \"mov r30, %A1" "\n\t" \"elpm" "\n\t" \"mov %0, r0" "\n\t" \: "=r" (__result) \: "r" (__addr32), \"I" (_SFR_IO_ADDR(RAMPZ)) \

: "r0", "r30", "r31" $; \__result; \

}))

25.36.1.2 #define __ELPM_dword_enhanced__( addr )

Value:


"out %2, %C1" "\n\t" \"movw r30, %1" "\n\t" \"elpm %A0, Z+" "\n\t" \"elpm %B0, Z+" "\n\t" \"elpm %C0, Z+" "\n\t" \"elpm %D0, Z" "\n\t" \: "=r" (__result) \: "r" (__addr32), \"I" (_SFR_IO_ADDR(RAMPZ)) \

: "r30", "r31" \); \__result; \

}))

25.36.1.3 #define __ELPM_dword_xmega__( addr )

Value:


"in __tmp_reg__, %2" "\n\t" \"out %2, %C1" "\n\t" \"movw r30, %1" "\n\t" \"elpm %A0, Z+" "\n\t" \"elpm %B0, Z+" "\n\t" \"elpm %C0, Z+" "\n\t" \"elpm %D0, Z" "\n\t" \"out %2, __tmp_reg__" \: "=r" (__result) \: "r" (__addr32), \"I" (_SFR_IO_ADDR(RAMPZ)) \

: "r30", "r31" \); \__result; \

}))



25.36.1.4 #define __ELPM_enhanced__( addr )

Value:


"out %2, %C1" "\n\t" \"movw r30, %1" "\n\t" \"elpm %0, Z+" "\n\t" \: "=r" (__result) \: "r" (__addr32), \

"I" (_SFR_IO_ADDR(RAMPZ)) \: "r30", "r31" \

); \__result; \

}))

25.36.1.5 #define __ELPM_float_enhanced__( addr )

Value:

(__extension__({ \uint32_t __addr32 = (uint32_t)(addr); \float __result; \__asm__ __volatile__ $ \

"out %2, %C1" "\n\t" \"movw r30, %1" "\n\t" \"elpm %A0, Z+" "\n\t" \"elpm %B0, Z+" "\n\t" \"elpm %C0, Z+" "\n\t" \"elpm %D0, Z" "\n\t" \: "=r" (__result) \: "r" (__addr32), \"I" (_SFR_IO_ADDR(RAMPZ)) \

: "r30", "r31" $; \__result; \

}))

25.36.1.6 #define __ELPM_float_xmega__( addr )

Value:


"in __tmp_reg__, %2" "\n\t" \"out %2, %C1" "\n\t" \"movw r30, %1" "\n\t" \"elpm %A0, Z+" "\n\t" \"elpm %B0, Z+" "\n\t" \"elpm %C0, Z+" "\n\t" \"elpm %D0, Z" "\n\t" \"out %2, __tmp_reg__" \: "=r" (__result) \: "r" (__addr32), \"I" (_SFR_IO_ADDR(RAMPZ)) \

: "r30", "r31" \); \__result; \

}))

25.36.1.7 #define __ELPM_word_classic__( addr )

Value:


338 CONTENTS


"out %2, %C1" "\n\t" \"mov r31, %B1" "\n\t" \"mov r30, %A1" "\n\t" \"elpm" "\n\t" \"mov %A0, r0" "\n\t" \"in r0, %2" "\n\t" \"adiw r30, 1" "\n\t" \"adc r0, __zero_reg__" "\n\t" \"out %2, r0" "\n\t" \"elpm" "\n\t" \"mov %B0, r0" "\n\t" \: "=r" (__result) \: "r" (__addr32), \"I" (_SFR_IO_ADDR(RAMPZ)) \

: "r0", "r30", "r31" \); \__result; \

}))

25.36.1.8 #define __ELPM_word_enhanced__( addr )

Value:


"out %2, %C1" "\n\t" \"movw r30, %1" "\n\t" \"elpm %A0, Z+" "\n\t" \"elpm %B0, Z" "\n\t" \: "=r" (__result) \: "r" (__addr32), \"I" (_SFR_IO_ADDR(RAMPZ)) \

: "r30", "r31" \); \__result; \

}))

25.36.1.9 #define __ELPM_word_xmega__( addr )

Value:


"in __tmp_reg__, %2" "\n\t" \"out %2, %C1" "\n\t" \"movw r30, %1" "\n\t" \"elpm %A0, Z+" "\n\t" \"elpm %B0, Z" "\n\t" \"out %2, __tmp_reg__" \: "=r" (__result) \: "r" (__addr32), \"I" (_SFR_IO_ADDR(RAMPZ)) \

: "r30", "r31" \); \__result; \

}))

25.36.1.10 #define __ELPM_xmega__( addr )

Value:




"in __tmp_reg__, %2" "\n\t" \"out %2, %C1" "\n\t" \"movw r30, %1" "\n\t" \"elpm %0, Z+" "\n\t" \"out %2, __tmp_reg__" \: "=r" (__result) \: "r" (__addr32), \

"I" (_SFR_IO_ADDR(RAMPZ)) \: "r30", "r31" \

); \__result; \

}))

25.36.1.11 #define __LPM_classic__( addr )

Value:


"lpm" "\n\t" \"mov %0, r0" "\n\t" \: "=r" (__result) \: "z" (__addr16) \: "r0" \

); \__result; \

}))

25.36.1.12 #define __LPM_dword_classic__( addr )

Value:


"lpm" "\n\t" \"mov %A0, r0" "\n\t" \"adiw r30, 1" "\n\t" \"lpm" "\n\t" \"mov %B0, r0" "\n\t" \"adiw r30, 1" "\n\t" \"lpm" "\n\t" \"mov %C0, r0" "\n\t" \"adiw r30, 1" "\n\t" \"lpm" "\n\t" \"mov %D0, r0" "\n\t" \: "=r" (__result), "=z" (__addr16) \: "1" (__addr16) \: "r0" \

); \__result; \

}))

25.36.1.13 #define __LPM_dword_enhanced__( addr )

Value:

(__extension__({ \uint16_t __addr16 = (uint16_t)(addr); \uint32_t __result; \


340 CONTENTS

__asm__ __volatile__ \( \

"lpm %A0, Z+" "\n\t" \"lpm %B0, Z+" "\n\t" \"lpm %C0, Z+" "\n\t" \"lpm %D0, Z" "\n\t" \: "=r" (__result), "=z" (__addr16) \: "1" (__addr16) \

); \__result; \

}))

25.36.1.14 #define __LPM_enhanced__( addr )

Value:


"lpm %0, Z" "\n\t" \: "=r" (__result) \: "z" (__addr16) \

); \__result; \

}))

25.36.1.15 #define __LPM_float_classic__( addr )

Value:


"lpm" "\n\t" \"mov %A0, r0" "\n\t" \"adiw r30, 1" "\n\t" \"lpm" "\n\t" \"mov %B0, r0" "\n\t" \"adiw r30, 1" "\n\t" \"lpm" "\n\t" \"mov %C0, r0" "\n\t" \"adiw r30, 1" "\n\t" \"lpm" "\n\t" \"mov %D0, r0" "\n\t" \: "=r" (__result), "=z" (__addr16) \: "1" (__addr16) \: "r0" \

); \__result; \

}))

25.36.1.16 #define __LPM_float_enhanced__( addr )

Value:


"lpm %A0, Z+" "\n\t" \"lpm %B0, Z+" "\n\t" \"lpm %C0, Z+" "\n\t" \"lpm %D0, Z" "\n\t" \: "=r" (__result), "=z" (__addr16) \: "1" (__addr16) \


25.37 power.h File Reference 341

); \__result; \

}))

25.36.1.17 #define __LPM_word_classic__( addr )

Value:


"lpm" "\n\t" \"mov %A0, r0" "\n\t" \"adiw r30, 1" "\n\t" \"lpm" "\n\t" \"mov %B0, r0" "\n\t" \: "=r" (__result), "=z" (__addr16) \: "1" (__addr16) \: "r0" \

); \__result; \

}))

25.36.1.18 #define __LPM_word_enhanced__( addr )

Value:


"lpm %A0, Z+" "\n\t" \"lpm %B0, Z" "\n\t" \: "=r" (__result), "=z" (__addr16) \: "1" (__addr16) \

); \__result; \

}))

25.36.1.19 #define pgm_get_far_address( var )

Value:

({ \uint_farptr_t tmp; \

\__asm__ __volatile__( \

\"ldi %A0, lo8(%1)" "\n\t" \"ldi %B0, hi8(%1)" "\n\t" \"ldi %C0, hh8(%1)" "\n\t" \"clr %D0" "\n\t" \

: \"=d" (tmp) \

: \"p" (&(var)) \

); \tmp; \

})

25.37 power.h File Reference

Macros

• #define clock_prescale_get() (clock_div_t)(CLKPR & (uint8_t)((1<<CLKPS0)|(1<<CLKPS1)|(1<<CLKP←↩S2)|(1<<CLKPS3)))


342 CONTENTS

Enumerations

• enum clock_div_t {clock_div_1 = 0, clock_div_2 = 1, clock_div_4 = 2, clock_div_8 = 3,clock_div_16 = 4, clock_div_32 = 5, clock_div_64 = 6, clock_div_128 = 7,clock_div_256 = 8 }

Functions

• static __inline__ void clock_prescale_set (clock_div_t) __attribute__((__always_inline__))

25.38 setbaud.h File Reference

Macros

• #define BAUD_TOL 2• #define UBRR_VALUE• #define UBRRL_VALUE• #define UBRRH_VALUE• #define USE_2X 0

25.39 setjmp.h File Reference

Macros

• #define __ATTR_NORETURN__ __attribute__((__noreturn__))

Functions

• int setjmp (jmp_buf __jmpb)• void longjmp (jmp_buf __jmpb, int __ret) __ATTR_NORETURN__

25.40 signature.h File Reference

25.41 sleep.h File Reference

Macros

• #define _SLEEP_CONTROL_REG MCUCR• #define _SLEEP_ENABLE_MASK _BV(SE)

Functions

• void sleep_enable (void)• void sleep_disable (void)• void sleep_cpu (void)• void sleep_mode (void)• void sleep_bod_disable (void)


25.42 stdint.h File Reference 343

25.42 stdint.h File Reference

Macros

• #define __USING_MINT8 0• #define __CONCATenate(left, right) left ## right• #define __CONCAT(left, right) __CONCATenate(left, right)

Limits of specified-width integer types

C++ implementations should define these macros only when __STDC_LIMIT_MACROS is defined before <stdint.←↩h> is included

• #define INT8_MAX 0x7f• #define INT8_MIN (-INT8_MAX - 1)• #define UINT8_MAX (INT8_MAX ∗ 2 + 1)• #define INT16_MAX 0x7fff• #define INT16_MIN (-INT16_MAX - 1)• #define UINT16_MAX (__CONCAT(INT16_MAX, U) ∗ 2U + 1U)• #define INT32_MAX 0x7fffffffL• #define INT32_MIN (-INT32_MAX - 1L)• #define UINT32_MAX (__CONCAT(INT32_MAX, U) ∗ 2UL + 1UL)• #define INT64_MAX 0x7fffffffffffffffLL• #define INT64_MIN (-INT64_MAX - 1LL)• #define UINT64_MAX (__CONCAT(INT64_MAX, U) ∗ 2ULL + 1ULL)

Limits of minimum-width integer types

• #define INT_LEAST8_MAX INT8_MAX• #define INT_LEAST8_MIN INT8_MIN• #define UINT_LEAST8_MAX UINT8_MAX• #define INT_LEAST16_MAX INT16_MAX• #define INT_LEAST16_MIN INT16_MIN• #define UINT_LEAST16_MAX UINT16_MAX• #define INT_LEAST32_MAX INT32_MAX• #define INT_LEAST32_MIN INT32_MIN• #define UINT_LEAST32_MAX UINT32_MAX• #define INT_LEAST64_MAX INT64_MAX• #define INT_LEAST64_MIN INT64_MIN• #define UINT_LEAST64_MAX UINT64_MAX

Limits of fastest minimum-width integer types

• #define INT_FAST8_MAX INT8_MAX• #define INT_FAST8_MIN INT8_MIN• #define UINT_FAST8_MAX UINT8_MAX• #define INT_FAST16_MAX INT16_MAX• #define INT_FAST16_MIN INT16_MIN• #define UINT_FAST16_MAX UINT16_MAX• #define INT_FAST32_MAX INT32_MAX• #define INT_FAST32_MIN INT32_MIN• #define UINT_FAST32_MAX UINT32_MAX• #define INT_FAST64_MAX INT64_MAX• #define INT_FAST64_MIN INT64_MIN• #define UINT_FAST64_MAX UINT64_MAX

Limits of integer types capable of holding object pointers


344 CONTENTS

• #define INTPTR_MAX INT16_MAX• #define INTPTR_MIN INT16_MIN• #define UINTPTR_MAX UINT16_MAX

Limits of greatest-width integer types

• #define INTMAX_MAX INT64_MAX• #define INTMAX_MIN INT64_MIN• #define UINTMAX_MAX UINT64_MAX

Limits of other integer types

C++ implementations should define these macros only when __STDC_LIMIT_MACROS is defined before <stdint.←↩h> is included

• #define PTRDIFF_MAX INT16_MAX• #define PTRDIFF_MIN INT16_MIN• #define SIG_ATOMIC_MAX INT8_MAX• #define SIG_ATOMIC_MIN INT8_MIN• #define SIZE_MAX UINT16_MAX• #define WCHAR_MAX __WCHAR_MAX__• #define WCHAR_MIN __WCHAR_MIN__• #define WINT_MAX __WINT_MAX__• #define WINT_MIN __WINT_MIN__

Macros for integer constants

C++ implementations should define these macros only when __STDC_CONSTANT_MACROS is defined before<stdint.h> is included.

These definitions are valid for integer constants without suffix and for macros defined as integer constant withoutsuffix

• #define INT8_C(value) ((int8_t) value)• #define UINT8_C(value) ((uint8_t) __CONCAT(value, U))• #define INT16_C(value) value• #define UINT16_C(value) __CONCAT(value, U)• #define INT32_C(value) __CONCAT(value, L)• #define UINT32_C(value) __CONCAT(value, UL)• #define INT64_C(value) __CONCAT(value, LL)• #define UINT64_C(value) __CONCAT(value, ULL)• #define INTMAX_C(value) __CONCAT(value, LL)• #define UINTMAX_C(value) __CONCAT(value, ULL)

Typedefs

Exact-width integer types

Integer types having exactly the specified width

• typedef signed char int8_t• typedef unsigned char uint8_t• typedef signed int int16_t• typedef unsigned int uint16_t• typedef signed long int int32_t• typedef unsigned long int uint32_t• typedef signed long long int int64_t• typedef unsigned long long int uint64_t


25.43 stdio.h File Reference 345

Integer types capable of holding object pointers

These allow you to declare variables of the same size as a pointer.

• typedef int16_t intptr_t• typedef uint16_t uintptr_t

Minimum-width integer types

Integer types having at least the specified width

• typedef int8_t int_least8_t• typedef uint8_t uint_least8_t• typedef int16_t int_least16_t• typedef uint16_t uint_least16_t• typedef int32_t int_least32_t• typedef uint32_t uint_least32_t• typedef int64_t int_least64_t• typedef uint64_t uint_least64_t

Fastest minimum-width integer types

Integer types being usually fastest having at least the specified width

• typedef int8_t int_fast8_t• typedef uint8_t uint_fast8_t• typedef int16_t int_fast16_t• typedef uint16_t uint_fast16_t• typedef int32_t int_fast32_t• typedef uint32_t uint_fast32_t• typedef int64_t int_fast64_t• typedef uint64_t uint_fast64_t

Greatest-width integer types

Types designating integer data capable of representing any value of any integer type in the corresponding signed orunsigned category

• typedef int64_t intmax_t• typedef uint64_t uintmax_t

25.43 stdio.h File Reference

Macros

• #define __need_NULL• #define __need_size_t• #define stdin (__iob[0])• #define stdout (__iob[1])• #define stderr (__iob[2])• #define EOF (-1)• #define fdev_set_udata(stream, u) do { (stream)->udata = u; } while(0)• #define fdev_get_udata(stream) ((stream)->udata)• #define fdev_setup_stream(stream, put, get, rwflag)• #define _FDEV_SETUP_READ __SRD• #define _FDEV_SETUP_WRITE __SWR• #define _FDEV_SETUP_RW (__SRD|__SWR)


346 CONTENTS

• #define _FDEV_ERR (-1)• #define _FDEV_EOF (-2)• #define FDEV_SETUP_STREAM(put, get, rwflag)• #define fdev_close()• #define putc(__c, __stream) fputc(__c, __stream)• #define putchar(__c) fputc(__c, stdout)• #define getc(__stream) fgetc(__stream)• #define getchar() fgetc(stdin)• #define BUFSIZ 1024• #define _IONBF 0• #define SEEK_SET 0• #define SEEK_CUR 1• #define SEEK_END 2

Typedefs

• typedef struct __file FILE• typedef long long fpos_t

Functions

• int fclose (FILE ∗__stream)• int vfprintf (FILE ∗__stream, const char ∗__fmt, va_list __ap)• int vfprintf_P (FILE ∗__stream, const char ∗__fmt, va_list __ap)• int fputc (int __c, FILE ∗__stream)• int printf (const char ∗__fmt,...)• int printf_P (const char ∗__fmt,...)• int vprintf (const char ∗__fmt, va_list __ap)• int sprintf (char ∗__s, const char ∗__fmt,...)• int sprintf_P (char ∗__s, const char ∗__fmt,...)• int snprintf (char ∗__s, size_t __n, const char ∗__fmt,...)• int snprintf_P (char ∗__s, size_t __n, const char ∗__fmt,...)• int vsprintf (char ∗__s, const char ∗__fmt, va_list ap)• int vsprintf_P (char ∗__s, const char ∗__fmt, va_list ap)• int vsnprintf (char ∗__s, size_t __n, const char ∗__fmt, va_list ap)• int vsnprintf_P (char ∗__s, size_t __n, const char ∗__fmt, va_list ap)• int fprintf (FILE ∗__stream, const char ∗__fmt,...)• int fprintf_P (FILE ∗__stream, const char ∗__fmt,...)• int fputs (const char ∗__str, FILE ∗__stream)• int fputs_P (const char ∗__str, FILE ∗__stream)• int puts (const char ∗__str)• int puts_P (const char ∗__str)• size_t fwrite (const void ∗__ptr, size_t __size, size_t __nmemb, FILE ∗__stream)• int fgetc (FILE ∗__stream)• int ungetc (int __c, FILE ∗__stream)• char ∗ fgets (char ∗__str, int __size, FILE ∗__stream)• char ∗ gets (char ∗__str)• size_t fread (void ∗__ptr, size_t __size, size_t __nmemb, FILE ∗__stream)• void clearerr (FILE ∗__stream)• int feof (FILE ∗__stream)


25.44 stdlib.h File Reference 347

• int ferror (FILE ∗__stream)

• int vfscanf (FILE ∗__stream, const char ∗__fmt, va_list __ap)

• int vfscanf_P (FILE ∗__stream, const char ∗__fmt, va_list __ap)

• int fscanf (FILE ∗__stream, const char ∗__fmt,...)

• int fscanf_P (FILE ∗__stream, const char ∗__fmt,...)

• int scanf (const char ∗__fmt,...)

• int scanf_P (const char ∗__fmt,...)

• int vscanf (const char ∗__fmt, va_list __ap)

• int sscanf (const char ∗__buf, const char ∗__fmt,...)

• int sscanf_P (const char ∗__buf, const char ∗__fmt,...)

• int fflush (FILE ∗stream)

• int fgetpos (FILE ∗stream, fpos_t ∗pos)

• FILE ∗ fopen (const char ∗path, const char ∗mode)

• FILE ∗ freopen (const char ∗path, const char ∗mode, FILE ∗stream)

• FILE ∗ fdopen (int, const char ∗)• int fseek (FILE ∗stream, long offset, int whence)

• int fsetpos (FILE ∗stream, fpos_t ∗pos)

• long ftell (FILE ∗stream)

• int fileno (FILE ∗)• void perror (const char ∗s)

• int remove (const char ∗pathname)

• int rename (const char ∗oldpath, const char ∗newpath)

• void rewind (FILE ∗stream)

• void setbuf (FILE ∗stream, char ∗buf)

• int setvbuf (FILE ∗stream, char ∗buf, int mode, size_t size)

• FILE ∗ tmpfile (void)

• char ∗ tmpnam (char ∗s)

25.44 stdlib.h File Reference

Data Structures

• struct div_t

• struct ldiv_t

Macros

• #define __need_NULL• #define __need_size_t• #define __need_wchar_t• #define __ptr_t void ∗• #define RAND_MAX 0x7FFF

Typedefs

• typedef int(∗ __compar_fn_t )(const void ∗, const void ∗)


348 CONTENTS

Functions

• void abort (void) __ATTR_NORETURN__

• int abs (int __i)

• long labs (long __i)

• void ∗ bsearch (const void ∗__key, const void ∗__base, size_t __nmemb, size_t __size, int(∗__compar)(constvoid ∗, const void ∗))

• div_t div (int __num, int __denom) __asm__("__divmodhi4")

• ldiv_t ldiv (long __num, long __denom) __asm__("__divmodsi4")

• void qsort (void ∗__base, size_t __nmemb, size_t __size, __compar_fn_t __compar)

• long strtol (const char ∗__nptr, char ∗∗__endptr, int __base)

• unsigned long strtoul (const char ∗__nptr, char ∗∗__endptr, int __base)

• long atol (const char ∗__s) __ATTR_PURE__

• int atoi (const char ∗__s) __ATTR_PURE__

• void exit (int __status) __ATTR_NORETURN__

• void ∗ malloc (size_t __size) __ATTR_MALLOC__

• void free (void ∗__ptr)

• void ∗ calloc (size_t __nele, size_t __size) __ATTR_MALLOC__

• void ∗ realloc (void ∗__ptr, size_t __size) __ATTR_MALLOC__

• double strtod (const char ∗__nptr, char ∗∗__endptr)

• double atof (const char ∗__nptr)

• int rand (void)

• void srand (unsigned int __seed)

• int rand_r (unsigned long ∗__ctx)

• int atexit (void(∗)(void))

• int system (const char ∗)• char ∗ getenv (const char ∗)

Variables

• size_t __malloc_margin

• char ∗ __malloc_heap_start

• char ∗ __malloc_heap_end

Non-standard (i.e. non-ISO C) functions.

• #define RANDOM_MAX 0x7FFFFFFF

• char ∗ itoa (int val, char ∗s, int radix)

• char ∗ ltoa (long val, char ∗s, int radix)

• char ∗ utoa (unsigned int val, char ∗s, int radix)

• char ∗ ultoa (unsigned long val, char ∗s, int radix)

• long random (void)

• void srandom (unsigned long __seed)

• long random_r (unsigned long ∗__ctx)


25.45 strcasecmp.S File Reference 349

Conversion functions for double arguments.

Note that these functions are not located in the default library, libc.a, but in the mathematical library, libm.a. Sowhen linking the application, the -lm option needs to be specified.

• #define DTOSTR_ALWAYS_SIGN 0x01 /∗ put ’+’ or ’ ’ for positives ∗/• #define DTOSTR_PLUS_SIGN 0x02 /∗ put ’+’ rather than ’ ’ ∗/• #define DTOSTR_UPPERCASE 0x04 /∗ put ’E’ rather ’e’ ∗/• #define EXIT_SUCCESS 0

• #define EXIT_FAILURE 1

• char ∗ dtostre (double __val, char ∗__s, unsigned char __prec, unsigned char __flags)

• char ∗ dtostrf (double __val, signed char __width, unsigned char __prec, char ∗__s)

25.45 strcasecmp.S File Reference

25.46 strcasecmp_P.S File Reference

25.47 strcasestr.S File Reference

25.48 strcat.S File Reference

25.49 strcat_P.S File Reference

25.50 strchr.S File Reference

25.51 strchr_P.S File Reference

25.52 strchrnul.S File Reference

25.53 strchrnul_P.S File Reference

25.54 strcmp.S File Reference

25.55 strcmp_P.S File Reference

25.56 strcpy.S File Reference

25.57 strcpy_P.S File Reference

25.58 strcspn.S File Reference

25.59 strcspn_P.S File Reference

25.60 strdup.c File Reference

Functions

• char ∗ strdup (const char ∗s1)


350 CONTENTS

25.61 string.h File Reference

Macros

• #define __need_NULL• #define __need_size_t• #define __ATTR_PURE__ __attribute__((__pure__))• #define _FFS(x)

Functions

• int ffs (int __val)• int ffsl (long __val)• __extension__ int ffsll (long long __val)• void ∗ memccpy (void ∗, const void ∗, int, size_t)• void ∗ memchr (const void ∗, int, size_t) __ATTR_PURE__• int memcmp (const void ∗, const void ∗, size_t) __ATTR_PURE__• void ∗ memcpy (void ∗, const void ∗, size_t)• void ∗ memmem (const void ∗, size_t, const void ∗, size_t) __ATTR_PURE__• void ∗ memmove (void ∗, const void ∗, size_t)• void ∗ memrchr (const void ∗, int, size_t) __ATTR_PURE__• void ∗ memset (void ∗, int, size_t)• char ∗ strcat (char ∗, const char ∗)• char ∗ strchr (const char ∗, int) __ATTR_PURE__• char ∗ strchrnul (const char ∗, int) __ATTR_PURE__• int strcmp (const char ∗, const char ∗) __ATTR_PURE__• char ∗ strcpy (char ∗, const char ∗)• int strcasecmp (const char ∗, const char ∗) __ATTR_PURE__• char ∗ strcasestr (const char ∗, const char ∗) __ATTR_PURE__• size_t strcspn (const char ∗__s, const char ∗__reject) __ATTR_PURE__• char ∗ strdup (const char ∗s1)• size_t strlcat (char ∗, const char ∗, size_t)• size_t strlcpy (char ∗, const char ∗, size_t)• size_t strlen (const char ∗) __ATTR_PURE__• char ∗ strlwr (char ∗)• char ∗ strncat (char ∗, const char ∗, size_t)• int strncmp (const char ∗, const char ∗, size_t) __ATTR_PURE__• char ∗ strncpy (char ∗, const char ∗, size_t)• int strncasecmp (const char ∗, const char ∗, size_t) __ATTR_PURE__• size_t strnlen (const char ∗, size_t) __ATTR_PURE__• char ∗ strpbrk (const char ∗__s, const char ∗__accept) __ATTR_PURE__• char ∗ strrchr (const char ∗, int) __ATTR_PURE__• char ∗ strrev (char ∗)• char ∗ strsep (char ∗∗, const char ∗)• size_t strspn (const char ∗__s, const char ∗__accept) __ATTR_PURE__• char ∗ strstr (const char ∗, const char ∗) __ATTR_PURE__• char ∗ strtok (char ∗, const char ∗)• char ∗ strtok_r (char ∗, const char ∗, char ∗∗)• char ∗ strupr (char ∗)• int strcoll (const char ∗s1, const char ∗s2)• char ∗ strerror (int errnum)• size_t strxfrm (char ∗dest, const char ∗src, size_t n)


25.62 strlcat.S File Reference 351

25.62 strlcat.S File Reference

25.63 strlcat_P.S File Reference

25.64 strlcpy.S File Reference

25.65 strlcpy_P.S File Reference

25.66 strlen.S File Reference

25.67 strlen_P.S File Reference

25.68 strlwr.S File Reference

25.69 strncasecmp.S File Reference

25.70 strncasecmp_P.S File Reference

25.71 strncat.S File Reference

25.72 strncat_P.S File Reference

25.73 strncmp.S File Reference

25.74 strncmp_P.S File Reference

25.75 strncpy.S File Reference

25.76 strncpy_P.S File Reference

25.77 strnlen.S File Reference

25.78 strnlen_P.S File Reference

25.79 strpbrk.S File Reference

25.80 strpbrk_P.S File Reference

25.81 strrchr.S File Reference

25.82 strrchr_P.S File Reference

25.83 strrev.S File Reference

25.84 strsep.S File Reference

25.85 strsep_P.S File Reference


352 CONTENTS

25.86 strspn.S File Reference

25.87 strspn_P.S File Reference

25.88 strstr.S File Reference

25.89 strstr_P.S File Reference

25.90 strtok.c File Reference

Functions

• char ∗ strtok (char ∗s, const char ∗delim)

Variables

• static char ∗ p

25.91 strtok_P.c File Reference

Functions

• char ∗ strtok_P (char ∗s, PGM_P delim)

25.92 strtok_r.S File Reference

25.93 strtok_rP.S File Reference

25.94 strupr.S File Reference

25.95 time.h File Reference

Data Structures

• struct tm

• struct week_date

Macros

• #define CLOCKS_PER_SEC ((clock_t) _CLOCKS_PER_SEC_)

• #define ONE_HOUR 3600

• #define ONE_DEGREE 3600

• #define ONE_DAY 86400

• #define UNIX_OFFSET 946684800

• #define NTP_OFFSET 3155673600


25.95 time.h File Reference 353

Typedefs

• typedef uint32_t time_t• typedef unsigned long clock_t

Enumerations

• enum _WEEK_DAYS_ {SUNDAY, MONDAY, TUESDAY, WEDNESDAY,THURSDAY, FRIDAY, SATURDAY }

• enum _MONTHS_ {JANUARY, FEBRUARY, MARCH, APRIL,MAY, JUNE, JULY, AUGUST,SEPTEMBER, OCTOBER, NOVEMBER, DECEMBER }

Functions

• time_t time (time_t ∗timer)• int32_t difftime (time_t time1, time_t time0)• clock_t clock (void)• time_t mktime (struct tm ∗timeptr)• time_t mk_gmtime (const struct tm ∗timeptr)• struct tm ∗ gmtime (const time_t ∗timer)• void gmtime_r (const time_t ∗timer, struct tm ∗timeptr)• struct tm ∗ localtime (const time_t ∗timer)• void localtime_r (const time_t ∗timer, struct tm ∗timeptr)• char ∗ asctime (const struct tm ∗timeptr)• void asctime_r (const struct tm ∗timeptr, char ∗buf)• char ∗ ctime (const time_t ∗timer)• void ctime_r (const time_t ∗timer, char ∗buf)• char ∗ isotime (const struct tm ∗tmptr)• void isotime_r (const struct tm ∗, char ∗)• size_t strftime (char ∗s, size_t maxsize, const char ∗format, const struct tm ∗timeptr)• void set_dst (int(∗)(const time_t ∗, int32_t ∗))• void set_zone (int32_t)• void set_system_time (time_t timestamp)• void system_tick (void)• uint8_t is_leap_year (int16_t year)• uint8_t month_length (int16_t year, uint8_t month)• uint8_t week_of_year (const struct tm ∗timeptr, uint8_t start)• uint8_t week_of_month (const struct tm ∗timeptr, uint8_t start)• struct week_date ∗ iso_week_date (int year, int yday)• void iso_week_date_r (int year, int yday, struct week_date ∗)• uint32_t fatfs_time (const struct tm ∗timeptr)• void set_position (int32_t latitude, int32_t longitude)• int16_t equation_of_time (const time_t ∗timer)• int32_t daylight_seconds (const time_t ∗timer)• time_t solar_noon (const time_t ∗timer)• time_t sun_rise (const time_t ∗timer)• time_t sun_set (const time_t ∗timer)


354 CONTENTS

• double solar_declination (const time_t ∗timer)• int8_t moon_phase (const time_t ∗timer)• unsigned long gm_sidereal (const time_t ∗timer)• unsigned long lm_sidereal (const time_t ∗timer)

Variables

• char ∗ _CLOCKS_PER_SEC_

25.96 twi.h File Reference

Macros

TWSR values

Mnemonics:TW_MT_xxx - master transmitterTW_MR_xxx - master receiverTW_ST_xxx - slave transmitterTW_SR_xxx - slave receiver

• #define TW_START 0x08• #define TW_REP_START 0x10• #define TW_MT_SLA_ACK 0x18• #define TW_MT_SLA_NACK 0x20• #define TW_MT_DATA_ACK 0x28• #define TW_MT_DATA_NACK 0x30• #define TW_MT_ARB_LOST 0x38• #define TW_MR_ARB_LOST 0x38• #define TW_MR_SLA_ACK 0x40• #define TW_MR_SLA_NACK 0x48• #define TW_MR_DATA_ACK 0x50• #define TW_MR_DATA_NACK 0x58• #define TW_ST_SLA_ACK 0xA8• #define TW_ST_ARB_LOST_SLA_ACK 0xB0• #define TW_ST_DATA_ACK 0xB8• #define TW_ST_DATA_NACK 0xC0• #define TW_ST_LAST_DATA 0xC8• #define TW_SR_SLA_ACK 0x60• #define TW_SR_ARB_LOST_SLA_ACK 0x68• #define TW_SR_GCALL_ACK 0x70• #define TW_SR_ARB_LOST_GCALL_ACK 0x78• #define TW_SR_DATA_ACK 0x80• #define TW_SR_DATA_NACK 0x88• #define TW_SR_GCALL_DATA_ACK 0x90• #define TW_SR_GCALL_DATA_NACK 0x98• #define TW_SR_STOP 0xA0• #define TW_NO_INFO 0xF8• #define TW_BUS_ERROR 0x00• #define TW_STATUS_MASK• #define TW_STATUS (TWSR & TW_STATUS_MASK)

R/∼W bit in SLA+R/W address field.

• #define TW_READ 1• #define TW_WRITE 0


25.97 wdt.h File Reference 355

25.97 wdt.h File Reference

Macros

• #define wdt_reset() __asm__ __volatile__ ("wdr")• #define _WD_PS3_MASK 0x00• #define _WD_CONTROL_REG WDT• #define _WD_CHANGE_BIT WDCE• #define wdt_enable(value)• #define wdt_disable()• #define WDTO_15MS 0• #define WDTO_30MS 1• #define WDTO_60MS 2• #define WDTO_120MS 3• #define WDTO_250MS 4• #define WDTO_500MS 5• #define WDTO_1S 6• #define WDTO_2S 7• #define WDTO_4S 8• #define WDTO_8S 9


Index

$PATH, 69$PREFIX, 69--prefix, 69

A more sophisticated project, 300A simple project, 288avrdude, usage, 99avrprog, usage, 99

Combining C and assembly source files, 285

Demo projects, 284disassembling, 291

FAQ, 48

installation, 69installation, avarice, 74installation, avr-libc, 72installation, avrdude, 73installation, avrprog, 73installation, binutils, 71installation, gcc, 72Installation, gdb, 73installation, simulavr, 73

supported devices, 2

tm, 317tools, optional, 70tools, required, 70

avr-libc - de Smith and Manuals/avr...ii CONTENTS Contents 1 AVR Libc 1 1.1 Introduction. . . . . ....

Documents

Transcript of avr-libc - de Smith and Manuals/avr...ii CONTENTS Contents 1 AVR Libc 1 1.1 Introduction. . . . . ....